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AN 

INAUGURAL  DISSERTATION 


ON 


CHEMICAL  CLASSIFICATION 


BY 


OLIVER  WOLCOTT  GIBBS,  A.M. 


AN 

INAUGURAL  DISSERTATION 

ON  A 

NATURAL   SYSTEM   OF  CHEMICAL   CLASSIFICATION. 

SUBMITTED  TO  THE  PUBLIC  EXAMINATION  OF  THE 

TRUSTEES  AND  OF  THE  FACULTY  OF  MEDICINE 
OF  THE  COLLEGE  OF  PHYSICIANS  AND  SURGEONS 

IN  THE  CITY  OF  NEW  YORK, 

Under  the  authority  of  the  Regents  of  the  University  of  the  State  of  New  York, 
ALEXANDER  H.  STEVENS,  M.D., 

PRESIDENT  OF  THE  COLLEGE  AND  OF  THE  BOARD  OF  TRUSTEES, 

FOR  THE  DEGREE  OF  DOCTOR  OF  MEDICINE, 
On  the  6th  day  of  February,  1845. 


By  OLIVER  WOLCOTT  GIBBS,  A.M. 

OF  THE   CITY  OF  NEW  YORK. 


PRINCETON,  N .  J . : 

PRINTED    BY   JOHN    T.   ROBINSON. 
1845. 


fit-  &f 


TO 

JOHN  TORREY,  M,B, 

PROFESSOR  OF  CHEMISTRY  AND  BOTANY 

IN  THE  COLLEGE  OF  PHYSICIANS  AND  SURGEONS. 

This  Dissertation  is  Respectfully  Inscribed. 


Natura  non  facit  saitum. 

Linnceut, 


INTRODUCTION. 


The  researches  of  chemists  have  resolved  all  known  forms 
of  matter  into  fifty-six  separate  and  distinct,  species,  which, 
having  thus  far  resisted  every  attempt  at  further  decomposi- 
tion are  termed  elements,  and  must  in  the  present  state  of  our 
knowledge  be  regarded  as  simple  substances.  These  Ele- 
ments united  in  various  proportions  and  with  various  degrees 
of  energy,  constituted  in  the  beginning  the  entire  mass  of  the 
Earth,  and  presented  an  Inorganic  Nature,  made  up  of  vast 
bodies  of  gaseous  and  liquid  matter,  as  well  as  of  many  suc- 
cessive series  of  rock,  and  of  innumerable  minerals,  amorphous, 
or  bounded  by  harmonious  and  symmetrically  disposed  planes, 
and  constituting  those  regular  figures  which  we  term  crystals. 
At  a  later  period  in  the  genesis  of  Nature,  the  mysterious 
power  of  Life  was  called  into  existence,  and  beginning  per- 
chance with  the  first  cell-germ  of  the  first  lichen,-  spread  at 
length  over  the  whole  Earth.  Then  innumerable  new  Forms 
came  into  being/  and  every  plant,  itself  built  up  particle  by 
particle  and  cell  by  cell  of  inorganic  matter,  became  a  labora- 
tory wherein  chemical  decompositions  and  recompositions 
were  perpetually  going  on  through  every  step  of  growth,  ma- 
turity and  decay.  At  a  still  late  rperiod  Life,  gathering  as  it 
were  new  energy  with  the  lapse  of  time,  passed  from  the 
highest  form  of  vegetable  to  the  lowest  form  of  animal  organ- 
izations, and  thence  upward  in  the  scale  of  being  through 
every  varying  type  and  form,  till  it  found  in  the  structure  of 
man  the  limit  beyond  which  it  was  not  destined  to  pass.  The 
new  and  more  complex  organisms  thus  created,  formed  out 


8  CHEMICAL  CLASSIFICATION. 

of  the  same  elements  new  and  more  complex  chemical  pro- 
ducts, adapted  to  their  growth,  their  structure  and  their  wants. 
The  animal  organism  found  in  that  of  the  plant,  nearly  all 
the  materials  necessary  for  its  own  sustenance  :  of  some  of 
these  it  changed  the  form  without  altering  the  chemical  com- 
position, while  of  others  again  it  moulded  the  composition  as 
well  as  the  form  anew.  And  when  at  length  Life  ceased  long- 
er to  exert  over  each  individual  its  plastic  force,  the  elements 
obeying  their  mutual  affinities  formed  new  and  simpler  pro- 
ducts, again  to  be  brought  under  the  sway  of  the  vital  force, 
and  thus  destined  to  pass  through  countless  cycles  of  change, 
and  to  appear  in  the  development  and  decay  of  myriads  of 
organized  forms.  Could  an  atom  of  Carbon  or  of  Hydrogen 
but  speak  to  us  what  a  history  might  it  not  unfold !  Through 
every  change  however  of  the  mineral,  the  plant,  and  the  ani- 
mal, the  one  universal  law  of  Chemical  combination — the  law 
of  definite  proportions— has  from  the  beginning  of  things, 
held  good.  Thus  then  we  are  led  to  recognize  two  great  de- 
partments of  Chemical  Science,  the  Chemistry  of  Unorganized 
and  the  Chemistry  of  Organized  bodies.  The  former  embraces 
all  those  combinations  which  take  place  under  the  operation 
of  purely  chemical  forces,  whether  in  the  laboratory  of  nature 
or  under  circumstances  determined  by  the  will  of  man.  The 
latter  comprehends  all  the  products  of  the  action  of  the  vital 
force  upon  inorganic  matter,  whether  this  action  be  immediate 
as  in  plants  or  mediate  as  in  animals,  together  with  those 
bodies  which  result  from  the  former  by  the  action  of  chemical 
reagents.  It  is  with  the  first  of  these  departments  that  we 
have  at  present  to  deal.  Between  the  fifty-six  elements  into 
which,  as  already  stated,  all  known  forms  of  matter  have  been 
resolved,  there  exist  numerous  remarkable  analogies,  which 
separate  them  first  into  subordinate  natural  families  or  groups, 
and  then  by  general  though  not  indistinct  resemblances,  unite 
them  into  one  indissoluble  chain,  each  link  of  which  differs 
rather  in  degree  than  in  kind  from  its  fellow  on  either  side  ;  so 
that  the  whote  illustrates  in  unorganized  nature,  the  truth  of 


INTRODUCTION 


the  maxim  of  Linnaeus — Natura  non  facit  saltum,  nature  makes 
no  leaps.  And  this  then  we  assume  as  the  fundamental  idea 
and  central  point  of  our  Essay,  namely,  that  this  law  of  grades 
which  Linnaeus  announced  for  the  organized  kingdom  alone, 
is  an  universal  law,  and  prevails  as  well  among  lifeless  atoms 
as  among  living  beings,  and  in  the  simplest  crystals  as  well  as 
in  the  innumerable  complex  forms  in  which  Life  outwardly 
manifests  itself.  The  forms  of  nature  are  many,  but  Nature 
herself  is  one.  We  propose  then  in  the  following  pages  to 
trace  these  analogies  as  they  exist  between  those  forms  of 
matter  which  come  within  the  range  of  Inorganic  Chemistry? 
whether  these  be  simple  or  compound,  and  to  point  out  the 
most  remarkable  groups  which  such  analogies  constitute. 
The  time  and  the  occasion  will  not  permit  us  to  do  more, 
though  we  would  gladly  extend  our  survey  to  the  fertile  and 
as  yet  but  little  tilled  field  of  Organic  Chemistry.  Moreover, 
the  classification  of  organic  products  must  obviously  depend 
upon  a  prior  classification  of  the  elements  themselves,  and 
upon  an  accurate  knowledge  of  the  nature  and  characters  of 
those  compounds  which  are  united  in  virtue  of  chemical 
forces  alone.  By  a  chemical  compound  we  shall  of  course  un- 
derstand any  substance  whose  constituents  are  united  in  obe- 
dience to  the  laws  of  definite  proportions,  and  we  shall  gene- 
rally speaking  divide  compounds  into  binary,  ternary,  quater- 
nary, &c,  according  to  the  number  of  their  ultimate  or  of  their 
proximate  constituents.  We  may  for  the  sake  of  convenience 
consider  the  subject  under  three  heads  : 

1st.  The  analogies  between  simple  substances  and  their 
division  into  groups. 

2d.  The  analogies  between  compounds  and  their  division 
into  groups. 

3d.  The  analogies  between  simple  and  compound  bodies. 

Before  taking  up  the  special  consideration  of  the  several 
groups,  it  will  be  well  to  dwell  for  a  time  in  a  general  and 
concise  manner  upon  some  of  the  more  important  points  in 


10  CHEMICAL    CLASSIFICATION. 

which  the  analogies  about  to  be  pointed  out  may  subsist,  and 
first  then  of  the  equivalent  weights  or  combining  masses. 

1.  The  equivalents  of  a  number  of  the  elements  appear  to 
be  connected  together  by  simple  numerical  relations.  The 
list  of  such  instances  of  Isomerism  originally  given  by 
Dumas,  has  since  been  considerably  extended  by  Dr.  Kane, 
and  future  researches,  by  correcting  several  of  the  equivalents 
at  present  received,  will  probably  exhibit  other  cases  of  coin- 
cidence in  this  particular.  Even  now  as  we  shall  presently 
show,  we  may  without  straining  our  figures,  add  several  to 
the  list  of  instances  enumerated  by  the  last  mentioned  chemists. 
The  bodies  between  which  such  isomerisms  exist,  for  the  most 
part  resemble  each  other  strongly  in  their  chemical  properties  j 
and  general  relations,  notwithstanding  the  assertion  of  Dr. 
Kane  that  "  in  no  case  are  their  properties  more  different." 
The  equivalent,  numbers  of  very  many  compounds,  however, 
exhibit  similar  coincidences,  without,  at  the  same  time,  accom- 
panying any  analogies  in  composition  or  in  chemical  character. 
Such  instances  must  of  course  be  regarded  as  accidental,  and 
must  not  be  suffered  in  any  degree  to  influence  our  systems  of 
arrangement  and  classification.  We  arrive  then  necessarily 
at  the  conclusion  that  the  chemical  properties  and  relations  of 
bodies  do  not  depend  upon  their  equivalent  weights  alone,  but 
that  in  addition  there  are  other  and  specific  forces  or  properties 
which  are  inseparably  connected  with  the  constitution  of  each, 
and  which  bestow  upon  each  its  distinctive  chemical  char- 
acter. 

2.  Admitting  that  the  specific  gravities  of  bodies  represent 
the  relative  weights  of  equal  bulks,  it  follows  that  if  we  divide 
the  specific  gravities  by  the  atomic  weights  or  equivalent  num- 
bers, we  obtain  the  relative  numbers  of  equivalents  which 
different  substances  contain  under  the  same  bulk  or  volume. 
The  numbers  thus  obtained  have  been  termed  by  the  German 
chemist  by  whom  they  were  first  observed,  the  Atomic  Num- 
bers, and  appear  to  be  deserving  of  more  attention  than  they 
have  as  yet  received.    The  atomic  numbers  of  the  elements 

c 


ATOMIC  NUMBERS.  It 

appear  to  be  connected  together  in  many  instances  by  simple 
ratios,  and  the  simple  substances  constituting  a  natural  group, 
have  usually  the  same  number  of  equivalents  contained  under 
the  same  volume.  The  requisite  data  for  instituting  a  com- 
parison between  the  atomic  numbers  of  compound  bodies  are 
for  the  most  part  wanting,  since  the  specific  gravities  of  very 
few  of  these  last  have  been  accurately  determined.  It  is  very 
much  to  be  regretted,  that  this  should  be  the  case,  since  the 
greater  the  number  of  equivalents  which  a  given  compound 
contains  under  a  given  volume,  the  greater  must  be  the  energy 
with  which  its  constituents  are  united  and  vice  versa,  so  that 
we  are  thus  apparently  furnished  with  an  accurate  method  of 
determining  Degrees  of  Affinity.  To  illustrate  this  by  an  ex- 
ample, let  us  take  the  case  of  Hydrate  of  Potassa  and  of 
monobasic  sulphate  of  water.  In  a  unit  of  volume  the  first 
of  these  bodies  contains  3032,  the  last  3766,  equivalents.  The 
formula  of  the  hydrate  of  Potassa  is  KO-f  HO,  that  of  the  sul- 
phate of  water  SO  3  -f-  HO.  Consequently  the  affinity  of  water 
for  sulphuric  acid  is  greater  than  the  affinity  of  water  for 
potassa,  in  the  proportion  of  3766  to  3032,  or  the  ratio  of  its 
affinity,  for  the  two  substances  may  be  expressed  by  the  frac- 
tion 1.2420.  In  like  manner  we  find  that  the  affinity  of  sul- 
phuric acid  for  water  is  greater  than  its  affinity  for  potassa,  in 
the  proportion  of  3766  to  2745,  so  that  if  the  principle  which 
we  have  laid  down  be  correct,  there  must  be  something  more 
than  a  mere  play  of  affinities  exerted  in  the  decomposition  of 
sulphate  water,  S03+HO,  by  hydrate  of  potassa,  KO  +  HO. 
As  a  general  rule,  the  greater  the  number  of  constituents  which 
any  substance  contains,  the  less  is  its  atomic  number,  and  it  is 
certain  that  a  compound  of  two  or  more  other  compounds, 
manifests  for  the  most  part  affinities  less  energetic  than  those 
of  either  of  its  constituents,  and  that  in  general  the  degree  of 
neutrality  is  directly  proportioned  to  the  complexity  of  the 
composition.  We  shall  endeavour  to  illustrate  this  position 
more  fully  hereafter,  when  treating  of  the  several  groups.  It 
will  be  sufficient  for  the  present  to  state  the  formula  and  the 


12  CHEMICAL   CLASSIFICATION. 

atomic  numbers  of  three  definite  sulphates  of  water,  and  of 
anhydrous  sulphuric  acid  ;  they  are  as  follows : 

S03— 4910 

HO  +  SO3— 3766 

2HO  +  S03— 3062 

SHO-fSOg—  2431 

No  connection  has  as  yet  been  traced  between  the  atomic 
numbers  of  a  compound  and  those  of  its  constituents.  A  con- 
nection however  of  some  kind  or  other  doubtless  exists,  and 
its  discovery  would  be  of  the  highest  interest  in  a  theoretic 
point  of  view. 

3.  Intimately  connected  with  the  atomic  numbers,  are  the 
Combining  Volumes,  or  the  relative  bulks  of  the  equivalents 
in  the  gaseous  state.  If  we  consider  the  space  occupied  by  an 
equivalent  of  Oxygen  as  unity,  then  an  equivalent  of  Chlorine, 
of  Iodine,  of  Bromine,  of  Hydrogen,  and  of  a  number  of  other 
bodies  both  simple  and  compound,  occupies  a  space  exactly 
twice  as  great.  The  equivalent  of  sulphur  on  the  other  hand, 
occupies,  in  the  state  of  gas,  but  one-third  the  space  which  is 
filled  by  an  equivalent  of  oxygen,  of  selenium,  and  of  tellu- 
rium. It  follows  therefore  that  in  one  unit  of  space,  there 
may  exist  3  equivalents  of  sulphur,  i  an  equivalent  of  chlo- 
rine or  of  hydrogen,  or  one  equivalent  of  oxygen,  selenium  or 
tellurium.  To  adopt  for  a  moment  the  language  of  the  ato- 
mic theory,  the  atom  of  chlorine  in  the  gaseous  state  is  twice 
as  large  as  the  atom  of  oxygen,  the  atom  of  sulphur  but  one- 
third  as  large,  and  so  on  for  all  other  bodies  simple  or  com- 
pound. The  atomic  volumes  of  all  bodies  then,  while  in  the 
gaseous  state,  are  connected  by  simple  numerical  ratios,  and 
this  fact  is  one  of  the  deepest  interest  and  importance.  Of  the 
56  elements  which  are  known  to  chemists,  but  a  small  propor- 
tion have  been  obtained  or  are  found  in  the  gaseous  state. 
The  combining  volumes  of  a  great  number  cannot  therefore 
be  experimentally  determined,  though  in  many  cases  they 
have  been  deduced  a  priori  from  clear  and  distinct  analogies. 
The  identity  of  two  or  more  substances  in  this  particular. 


ISOMORPHISM.  13 

does  not  necessarily  involve  a  similarity  in  general  chemical 
properties  and  relations  as  will  hereafter  be  ^hown. 

4.  By  a  process  exactly  the  reverse  of  that  employed  in 
obtaining  the  Atomic  Numbers,  namely,  by  dividing  the  equi- 
valent weights  by  the  specific  gravities,  Dr.  Kopp  has  ob- 
tained a  series  of  numbers  which  he  regards  as  expressing  the 
atomic  volumes  of  bodies;  or  in  other  words  the  relative 
volumes  of  their  atoms ;  and  he  considers  that  his  researches 
justify  the  conclusion  that  isomorphous  bodies  have  the  same 
atomic  volume.  The  apparent  deviations  from  this  law  ex- 
hibited by  many  isomorphous  bodies,  he  regards  as  aris- 
ing from  the  fact  that  substances  are  not  absolutely  iso- 
morphous but  only  approximately  so,  and  a  glance  at  the 
numbers  which  he  brings  forward  in  support  of  his  opinion, 
will  abundantly  justify  the  necessity  of  admitting  this  or  some 
similar  explanation. 

5.  Almost  every  unorganized  body  may  be  obtained  in  a 
crystalline  state,  and  may  consequently  be   arranged  under 
some  one  crystallographic  system,  and  have  its  interfacial  and 
interaxial  angles  determined  with  a  greater  or  less  degree  of 
accuracy.      If  now  we  institute  a  comparison  between  the 
crystalline  forms  of  different  substances  simple  or  compound, 
we  find  that  between  those  which  are  connected  together  by 
strong  chemical  analogies,  there  exists  also  certain  definite  re- 
lations of  form,  in  many  instances  approximating  toward  iden- 
tity.    A  natural  family  or  group  has  in  general  the  same  crys- 
talline as  well  as  the  same  chemical  types.     Identity  of  crys- 
talline form  however  by  no  means  necessarily  implies  analogy 
in  chemical  constitution,  since  a  substance  composed  of  a  great 
number  of  molecules  of  different  kinds  may  crystallize  in  the 
same  form  as  an  element,  and  since  on  the  other  hand  two 
elements  may  appear  in  crystallographic  systems  which  have 
no  connexion  with  each  other.     In  fine,  so  numerous  are  the 
instances  of  agreement  in  chemical  constitution  and  relations 
without,  a  corresponding  analogy  of  form,  and  again  of  a  coin- 
cidence in  crystalline  form  without  a  corresponding  agree- 

2 


14  CHEMICAL   CLASSIFICATION. 

ment  in  chemical  relations,  that  while  similarity  of  form  must 
ever  be  regarded  as  a  strong  reason  for  classifying  together 
bodies  which  are  otherwise  analogous,  yet  the  want  of  such  a 
similarity  will  never  of  itself  justify  the  separation  of  substances 
which  agree  in  their  general  chemical  relations.  It  is  the  too 
implicit  reliance  upon  analogy  of  form  which  renders  the 
classification  proposed  by  Graham  imperfect,  and  which  has 
led  him  to  associate  together  substances  which  differ  widely 
in  their  chemical  relations,  and  to  separate  others  between 
which  there  exists  in  these  respects  the  strongest  resemblance. 
Certain  bodies  are  met  with  crystallized  in  two  different  forms 
and  isomorphous  with  two  distinct  classes  or  groups  of  other 
substances.  Such  bodies  are  said  to  be  dimorphous,  and  serve 
to  connect  several  groups  together  at  once.  The  relatior^  of 
dimorphism  is  subject  to  the  same  restrictions  as  that  of  iso- 
morphism and  must  not  be  too  strongly  relied  upon  in  classi- 
fying and  arranging  substances  in  natural  families.  No  con- 
nection has  yet  been  traced  between  the  crystalline  form  of  a 
compound  and  the  crystalline  forms  of  its  constituents.  The 
problem  is  one  of  the  finest  which  offers  itself  to  the  enquiring 
mind,  in  the  whole  range  of  physical  science,  but  sufficient 
data  to  form  the  basis  of  the  solution  are  yet  wanting.  The 
chemical  and  physical  history  of  no  compound  can  be  consid- 
ered complete  without  an  accurate  and  scrupulous  determina- 
tion of  its  crystalline  form,  and  the  negligence  of  chemists  with 
regard  to  this  most  important  particular  cannot  be  too  strongly 
reprobated.  We  shall  hereafter  point  out  a  few  instances  in 
which  a  direct  relation  subsists  between  the  forms  of  a  com- 
pound and  the  forms  of  its  elements.  It  may  not  be  improper 
to  note  in  this  place  the  fact  that  as  a  general  rule,  the  simpler 
the  constitution  of  a  body,  the  simpler  also  is  its  crystalline 
form  and  vice  versa. 

6.  The  relations  of  bodies  to  heat,  though  not  sufficient  m 
themselves  to  furnish  grounds  for  associating  them  in  groups 
are  yet  of  very  great  interest  and  importance.  The  researches 
of  Begnault  and  of  Newmann  and  Awgadro,  have  recently 


ISOMORPHISMS.  15 

afforded  strong  confirmation  of  the  accuracy  of  Dulong  and 
Petit's  law,  that  the  specific  heats  of  equivalent  weights  of  sim- 
ple substances  are  equal.  The  few  cases  which  appear  to  be 
exceptions  to  this  law  may  easily  be  reconciled  with  it,  not  by 
an  arbitrary  subdivision  of  the  atomic  weights,  but  by  a  differ- 
ent enunciation  of  the  law  itself.  Thus  if  we  state  that  "  the 
specific  heats  of  the  elements  are  either  the  same  or  are  con- 
nected with  each  other  by  simple  multiples,"  we  obtain  a  clear 
and  satisfactory  explanation  of  the  discrepancies  which  have 
thrown  so  much  doubt  upon  the  existence  of  any  definite  law 
whatever,  and  which  have  led  to  so  many  alterations  of  the 
equivalents  and  to  so  many  improbable  hypotheses.  Between 
the  specific  heats  of  compound  bodies  there  exist,  also,  sim= 
ilar  relations,  though  they  have  not  as  yet  been  very  fully 
studied.  No  connexion  has  been  detected  between  the  fusing  or 
boiling  points  of  different  substances  whether  simple  or  com- 
pound and  their  chemical  constitution  or  relations ;  though  Ger- 
hardt  has  recently  succeeded  in  deducing  an  empirical  formula, 
by  which,  having  given  the  constitution  and  the  boiling  point  of 
one  liquid  hydrocarbon  and  the  constitution  of  a  second,  he  is 
able  to  determine  the  boiling  point  of  this  last,  by  calculation 
alone.  No  connexion  appears  to  subsist  between  the  fusing 
or  boiling  point  of  any  substance,  and  the  number  of  equiva- 
lents which  it  contains  in  the  unit  of  space.  The  quantity  of 
heat  which  is  developed  during  the  act  of  chemical  combina- 
tion appears  always  to  be  definite,  and  depends  upon  the  na- 
ture and  composition  of  the  substances  uniting.  The  subject 
however  has  not  yet  been  sufficiently  investigated  to  admit  of 
the  deduction  of  definite  laws.  The  same  remark  may  be 
made  with  regard  to  the  latent  heats  of  all  substances  what- 
ever. We  are  as  yet  very  imperfectly  acquainted  with  the 
subject.  Neither  the  conducting  powers  nor  the  expansibili- 
ties of  bodies  appear  to  be  connected  with  their  chemical  con- 
stitution. 

7.  Upon  the  consideration  of  the  electrical  relations  we  do 
not  propose  in  this  place  to  enter.     The  subject  is  as  yet  too 


16  CHEMICAL    CLASSIFICATION. 

little  understood  to  admit  of  anything  more  than  a  general  ap- 
plication of  these  relations  to  the  purpose  of  classification. 
We  shall  point  out  in  speaking  of  the  several  groups,  the  elec- 
trical conditions  of  each,  agreeably  to  the  theory  of  Faraday 
and  Berzelius,  though  we  do  not  propose  to  adopt  this  as  the 
basis  of  classification,  as  is  now  very  commonly  done. 

8.  The  influence  which  the  chemical  constitution  of  a  body 
exerts  upon  the  transmission,  reflection,  absorption  or  polari- 
zation of  Light,  has  hitherto  excited  very  little  attention.  No 
connexion  has  been  traced  between  the  refractive  power  of  a 
compound  and  the  refractive  powers  of  its  constituents,  and 
very  few  data  exist  with  which  to  institute  a  comparison- 
Possibly  the  action  of  bodies  upon  Light  may  be]  connected 
with  their  Atomic  Numbers,  but  the  whole  subject  is  involved 
in  the  deepest  obscurity  and  presents  a  noble  field  for  experi- 
mental research. 

9.  It  remains  to  consider  in  a  brief  and  general  manner,  the 
purely  chemical  relations  of  bodies  to  each  other,  that  is  to  say, 
the  relations  of  constitution,  of  acidity  and  basidity,  of  molecu- 
lar types  and  of  general  character  and  properties.  The  mole- 
cular type  of  any  substance  is  of  the  utmost  importance  in  the 
determination  of  the  group  to  which  it  belongs.  As  the  ele- 
ments are  to  the  best  of  our  knowledge  identical  in  this  partic- 
ular, we  are  obliged,  in  order  to  investigate  their  chemical  re- 
lations, to  examine  the  molecular  structure  of  the  compounds 
which  they  form  with  one  another,  and  from  these  to  deduce 
the  general  character  of  each.  We  find  then  that  a  natural 
group  of  Elements,  by  entering  into  combination  with  other 
elements,  forms  a  series  ot  compounds  whose  molecular  struc- 
tures are  precisely  similar  to  one  another,  and  which  may  be 
transformed  the  one  into  the  other  by  a  simple  change  in  the 
chemical  symbols  which  constitute  the  formulae.  In  like  man- 
ner a  natural  group  of  compound  bodies  is  composed  of  sub- 
stances which  are  exactly  parallel  to  one  another,  both  in  com- 
position and  in  the  arrangement  of  their  constituents.  Bodies 
which  are  similarly  constituted  exhibit  for  the  most  part  very 


GROUP    I.  17 

similar  relations  toward  other  bodies,  and  conversely  we  are 
often  able  to  decide  upon  the  constitution  of  a  body  by  the 
analogy  which  exists  between  its  properties  and  those  of  an- 
other substance  whose  composition  is  already  known.  The 
relations  of  acidity  and  basidity  depend  strictly  upon  molecu- 
lar type,  and  are  purely  relative,  a  substance  which  in  one 
connexion  is  an  acid,  is  in  another  a  base,  and  in  another 
again,  neutral.  The  neutrality  of  any  compound  is  for  the 
most  part  in  proportion  to  the  number  of  secondary  com- 
pounds of  which  it  is  composed,  neutrality  being  here  used  in 
the  sense  of  incapacity  to  enter  still  further  into  combination. 
Certain  of  the  elements  generate  by  uniting  with  other  ele- 
ments compounds,  which  are  either  acids  or  bases;  others 
again  generate  new  substances  which  are  eminently  neutral 
and  incapable  of  forming  new  compounds  with  one  another. 
The  union  of  certain  bodies  is  accompanied  with  the  develop- 
ment of  light  and  heat,  with  others  again  no  such  phenomena 
are  visible  during  the  act  of  combination.  Many  substances 
are  capable  of  uniting  directly  with  each  other,  when  brought 
together  in  a  free  state  and  at  ordinary  temperatures,  the  affin- 
ities of  others  again  must  be  modified  by  heat,  light  or  elec- 
tricity, before  they  can  be  made  to  combine.  Finally  the 
three  states  in  which  bodies  present  themselves,  as  solids, 
liquids  or  gases,  appear  to  depend  upon  their  relations  to  heat 
alone,  and  to  have  no  definite  relations  to  their  chemical  con- 
stitution or  properties. 

We  have  thus  taken  a  brief  survey  of  some  of  the  most 
important  points  in  which  the  chemical  analogies  of  bodies 
subsist,  and  we  now  proceed  to  the  consideration  of  the  sev- 
eral groups  which  are  constituted  by  the  elementary  substan- 
ces. 

GROUP  I. 

The  first  group  comprises  eight  elements.  Oxygen,  Sul- 
phur, Selenium,  Tellurium,  Chlorine,  Bromine,  Fluorine.  Be- 
tween these  eight  elements,  though  widely  different  in  the 


18  CHEMICAL  CLASSIFICATION. 

common  physical  properties  of  matter  there  exist  the  most 
intimate  chemical  relations,  so  that  as  a  whole  the  group  con- 
stituted by  them  is  more  strongly  marked  than  any  other. 
These  relations  are  as  follows  : 

1.  A  body  belonging  to  any  other  group  commonly  unites 
with  a  member  of  this,  with  that  evolution  of  light  and  heat 
which  chemists  term  combustion. 

2.  The  affinities  of  the  members  of  this  family  are  more 
energetic  and  are  exerted  through  a  wider  range  than  those 
of  any  other  family.  And  this  is  proved  by  the  number  and 
variety  of  the  compounds  which  they  form  with  other  sub- 
stances ;  by  their  combining,  as  a  general  rule,  at  much  lower 
temperatures  than  other  substances,  and  by  their  capacity  of 
entering  into  direct  combination,  while  in  a  free  state. 

3.  The  eight  elements  composing  this  group  are  capable  of 
replacing  each  other  in  a  compound  of  given  molecular  type 
without  altering  that  type,  and  without  altering,  otherwise 
than  in  degree,  the  chemical  relations  of  the  primitive  whence 
the  new  substances  are  by  substitution  derived.  The  new 
substances  will  be  acids,  bases  or  neutral,  according  as  that 
from  which  they  are  supposed  to  be  derived  was  acid,  base, 
or  neutral. 

4.  The  existence  of  any  particular  compound  or  compounds 
of  a  substance  not  belonging  to  group  1st,  with  any  member 
of  this  group,  is  an  a  priori  evidence,  that  there  may  also  ex- 
ist similar  compounds  of  the  other  members  of  group  1st  with 
the  substance  in  question.  Thus  the  different  groups  of  chlo- 
rides, oxides,  sulphides,  &c.  are  exactly  parallel  to  one  another 
in  composition,  and  as  already  remarked,  (3)  differ  in  their 
chemical  relations  only  in  degree. 

5.  A  compound  of  one  equivalent  of  a  member  of  this 
family,  with  one  equivalent  of  a  radical  simple  or  compound, 
performs  in  general  the  part  of  a  base,  though  as  already  re- 
marked one  base  may  act  the  part  of  an  acid  toward  another. 
As  the  number  of  equivalents  of  the  substance  belonging  to 
group   1st,  increases,  the  acidity  of  the  compound  also  in- 


GROUP   I.  19 

creases.  A  binoxide  or  bichloride  is  feebly  basic  toward  pow- 
erful oxacids  or  chloracids,  and  feebly  acid  toward  powerful 
oxy-bases  or  chlorobases.  A  teroxide  or  terchloride  is  in  almost 
all  cases  a  powerful  acid,  and  a  pentoxide  or  pentachloride 
still  more  so. 

6.  Substitutions  of  one  member  of  group  first  for  another 
may  be  either  complete  or  partial.  Thus  chlorine  may  either 
replace  3  equivalents  of  oxygen  in  a  teroxide,  or  only  one, 
We  meet  for  example  with  such  compounds  as  S02C1,  Cr02Cl, 
Fe202Cl,  COC1,  and  many  others  of  a  similar  constitution. 
Such  compounds  will  of  course  be  most  conveniently  classed 
with  the  substance  from  which  they  are  or  may  be  considered 
to  be  derived. 

7.  Between  the  equivalent  weights  of  several  members  of 
this  group  remarkable  relations  are  found  to  subsist.  Thus, 
Oxygen,  Sulphur,  and  Tellurium  appear  to  be  isomeric,  their 
equivalents  being  to  each  other  as  8, 16  and  64,  very  nearly,  or 
as  1,2  and  3.  Selenium  on  the  other  hand,  which  very  closely 
resembles  Sulphur  in  its  chemical  relations,  is  entirely  uncon- 
nected with  it  in  this  particular,  but  its  equivalent  is  very 

nearly  half  that  of  Bromine.  Se=39.63= /8,39=39.19=^  Br. 

2 

Chlorine,  Iodine  and  Bromine  do  not  appear  to  be  connected 
by  any  definite  relations  between  their  atomic  weights,  and 
future  researches  may  show  that  there  is  no  real  isomerism  be- 
tween Selenium  and  Bromine.* 

8.  The  combining  volumes  of  Oxygen,  Selenium  and  Tel* 
lurium  are  equal  to  each  other  and  are  represented  by  unity. 
The  combining  volume  of  Sulphur  is  3  times,  and  that  of 
Chlorine,  Iodine,  Bromine  and  Fluorine  twice,  as  great  as  that 
of  Oxygen.  Hence  either  the  atom  of  Chlorine  is  twice  as 
large  as  the  atom  of  Oxygen  or  else  Oxygen  contains  in  the 
same  space  twice  as  many  particles  or  atoms  as  Chlorine  does. 
This  last  is  perhaps  the  more  probable  opinion  of  the  two. 

*  According  to  Dumas,  the  equivalent  of  Selenium  is  40,  which  makes  it  iso- 
meric with  Oxygen:  8  X  5  =  40. 


20  CHEMICAL    CLASSIFICATION. 

9.  The  atomic  numbers  of  Chlorine,  Iodine  and  Bromine 
are  the  same,  that  is  to  say,  one  unit  of  space  contains  an  equal 
number  of  equivalents  of  each  of  these  substances.  The 
numbers  themselves  are,  Chlorine  383,  Bromine  380,  Iodine 
392,  the  mean  of  which  is  385,  which  may  therefore  be  con- 
sidered as  representing  the  true  atomic  number  of  the  3  sub- 
stances in  question.  The  atomic  numbers  of  Sulphur  and  Se- 
lenium are  apparently  unconnected ;  they  are,  of  Sulphur  125, 
of  Selenium  109.  As  Oxygen  has  not  been  obtained  in  a 
solid,  and  Fluorine  in  an  isolated  state,  their  atomic  numbers 
cannot  of  course  be  determined.  Tellurium  is  connected  nei- 
ther with  Chlorine  and  Bromine,  nor  with  Sulphur  or  Selenium 
by  any  very  certain  relations  of  atomic  numbers.  It  contains 
in  one  unit  of  space  978  equivalents,  which  is  very  nearly  9 
times  as  many  as  are  contained  within  the  same  volume  of  Se- 
lenium. 109x9  =  981  =  978  +  3.J 

10.  As  a  general  rule  an  oxide  appears  to  contain  under 
the  same  bulk  a  greater  number  of  equivalents  than  a  corres- 
ponding sulphide,  and  a  sulphide  a  greater  number  than  a  cor- 
responding chloride.  Such  at  least  is  the  conclusion  which 
the  writer  has  drawn  from  his  own  calculations  which  are  all 
which  he  has  had  to  rely  upon.  The  following  tables  will 
exhibit  this  to  a  limited  extent.  (Note.  The  specific  gravity 
of  water  is  here  taken  as  1000.) 

Pb=11030,  PbO  =  S504,  PbS  =  6336,  PbCl~ 4080,  Aq= 
9640,  AqO=6139,  AqCl=3894. 

Hg=13210,HgO=s  10119,  HgCl  =  3754,Hg202  =  8097,Hg 
2C1=2932. 

Perhaps  a  more  extended  induction  may  overthrow  the 
opinion  which  we  have  advanced  in  regard  to  the  atomic 
numbers  of  oxides,  sulphides  and  chlorides.  But  if  on  the 
contrary  more  accurate  and  extensive  observation  shall  de- 
monstrate its  correctness,  it  will  then  as  it  seems  to  us,  afford 
an  explanation  of  many  facts  in  the  history  of  these  bodies 
which  are  at  present  involved  in  obscurity.  For  does  not  a 
very  great  degree  of  condensation  imply  a  very  energetic  at- 


GROUP    I.  21 

traction  ?  and  does  not  a  lesser  degree  of  condensation  imply 
a  weaker  attraction  ?  The  subject  is  at  any  rate  worthy  of  a 
most  thorough  and  careful  study. 

11.  Between  the  atomic  volumes  of  certain  members  of 
this  group  there  also  exist  remarkable  relations.  Thus  by  di- 
viding the  atomic  weights  of  Chlorine,  Iodine  and  Bromine 
by  their  respective  specific  gravities  we  obtain  as  quotients, 
25,  25,  26,  and  we  therefore  conclude  that  the  atomic  volume 
or  the  bulk  of  the  equivalent  is  the  same  for  each  of  these 
bodies.  Thus  not  only  are  there  as  we  have  already  shown 
(9)  the  same  number  of  equivalents  in  the  same  bulk  of  each 
of  these  bodies,  but  the  bulk  or  volume  of  each  of  these  equiv- 
alents is  also  the  same.  And  this  last  is  by  no  means  a  ne- 
cessary consequence,  as  might  at  first  appear,  of  the  first.  For 
as  it  is  clear  that  matter,  whether  it  consist  of  atoms  or  not,  is 
not  continuous  through  space,  so  it  must  be  evident  that  one 
unit  of  space,  one  cubic  inch  for  example,  may  contain  either 
very  different  numbers  of  equal-sized  atoms  or  the  same  num- 
ber of  atoms  differing  in  size,  or  again,  different  numbers  of 
different  atoms,  provided  only  that  these  atoms  are  unequally 
distant  from  each  other  in  the  three  cases  which  we  have  sup- 
posed. The  volume  of  the  atom  of  Tellurium  is  to  the  volume 
of  the  atom  of  Sulphur  or  Selenium  as  10  to  8  or  as  5  to  4,  and 
to  the  volume  of  the  atom  of  Chlorine,  Iodine  or  Bromine  as 
10  to  25  or  2  to  5.  The  atomic  volumes  of  Oxygen  and  Flu- 
orine as  well  as  their  atomic  numbers  are  of  course  unknown. 

12.  Of  the  8  elements  which  compose  group  1st,  Sulphur 
and  Selenium  are  isomorphous.  Chlorine,  Bromine  and  Io- 
dine are  also  isomorphous,  and  possess  besides  the  same  atomic 
volume  and  the  same  atomic  number.  The  compounds  of 
Fluorine  are  also  uniformly  isomorphous  with  those  of  Chlo- 
rine, Iodine  and  Bromine,  and  we  have  therefore  strong  rea- 
sons for  regarding  Fluorine  as  itself  isomorphous  with  Chlo- 
rine, Iodine  and  Bromine.  Tellurium  is  not  connected  with 
the  other  members  of  Group  1st  by  isomorphism,  unless  in- 
deed it  should  prove  like  Sulphur  to  be  dimorphous.     Finally, 


22  CHEMICAL    CLASSIFICATION. 

the  crystalline  forms  of  the  sulphur  salts  have  not  been  suffi- 
ciently studied  to  enable  us  to  form  any  idea  of  the  crystalline 
form  of  Oxygen,  by  instituting  a  comparison  between  the  two 
classes  of  salts,  which  Sulphur  and  Oxygen  are  respectively 
capable  of  generating.  We  may  notice  in  this  connexion  a 
fact  which  does  not  seem  to  have  attracted  the  attention  of 
chemists.  The  crystals  of  many  anhydrous  protochlorides, 
protiodides,  protobromides,  and  protofluorides  belong  to  the 
regular  system,  being  for  the  most  part  either  cubes  or  regu- 
lar octahedra.  Furthermore,  the  crystals  of  many  double  pro- 
tochlorides,  double  protiodides,  &c.  are  also  met  with  in  the 
regular  system.  In  order  not  to  leave  this  assertion  without 
proof  or  illustration,  we  will  cite  the  formulae  of  a  few  com- 
pounds together  with  their  crystalline  forms. 

(KC1,  NaCl,  AqCl,  KI,  KB^  CaF,  NaF,  NaB3,)  cubes. 
(AqCl+KCl),  (AqCl  +  NaCl,  AqCl  +  HCl,)  cubes.  Manypro- 
tochlorides  and  protobromides  crystallize  with  water,  and  their 
form  is  thus  rendered  more  complex.  Other  relations  of  form 
and  composition  will  be  pointed  out  when  treating  of  other 
groups. 

13.  The  specific  heats  of  certain  of  the  elements  connected 
with  this  group  appear  to  bear  a  definite  relation  to  each  other. 
Thus  the  specific  heat  of  an  atom  of  Sulphur  being  consid- 
ered as  unity,  that  of  an  atom  or  equivalent  of  Tellurium  is 
represented  by  2,  or  is  twice  as  great,  that  of  Iodine  again  is 
4  times  as  great  as  that  of  Sulphur  and  twice  as  great  as  that 
of  Tellurium.  The  specific  heats  of  equivalent  weights  of  the 
other  members  of  group  1st  have  not  yet  been  accurately  de- 
termined. 

14.  The  elements  composing  this  group  are  more  highly 
electro-negative  than  any  other  substances  which  we  are  ac- 
quainted with.  In  the  electro-chemical  theory  they  constitute, 
par  excellence,  the  electro-negative  group,  and  they  are  sepa- 
rated from  the  other  groups  in  this  respect  by  a  wide  interval. 
If  a  compound  of  an  element  belonging  to  this  family  with 
one  belonging  to  any  other,  be  submitted  to  electrolysis,  the 


GROUP   I.  23 

constituent  belonging  to  the  first  group  will  always  be  found 
at  the  positive  pole,  that  belonging  to  any  other  group  will  on 
the  contrary  always  be  found  at  the  negative  pole.  An  elec- 
tro-negative element  is  termed  by  Graham,  Chlorous,  while  on 
the  other  hand  an  electro-positive  element  or  constituent  re- 
ceives the  appellation  of  Zincous.  The  different  members  of 
the  group  differ  in  the  degree  of  electro-negativeness,  but  our 
knowledge  of  the  subject  is  far  from  being  sufficiently  com- 
plete to  enable  us  to  form  a  scale  in  which  each  shall  find  its 
proper  place,  or  even  to  say  positively  which  of  the  elements 
is  most  highly  electro-negative,  and  which  again  is  at  the  other 
end  of  the  scale.  This  and  much  else  is  open  for  investiga- 
tion. 

15.  It  remains  to  consider  the  different  members  of  this 
group  in  their  relations  with  each  other.  With  the  exception 
of  Fluorine  and  of  course  Oxygen,  they  all  agree  in  forming 
with  Oxygen,  compounds  which  for  the  most  part  are  power- 
fully acid.  The  types  of  these  compounds  are  not  in  the  pre- 
sent state  of  our  knowledge  perfectly  parallel.  Sulphur  forms 
with  Oxygen  6  distinct  acids,  of  which  but  one,  namely,  hypo- 
sulphuric  acid  has  its  analogue  among  the  Oxygen  compounds 
of  Chlorine,  Iodine  and  Bromine,  while  two,  namely,  sulphur- 
ous and  sulphuric  acids,  have  analogues  among  the  com- 
pounds of  Selenium  and  Tellurium.  Chlorine  again  forms  4 
compounds  with  Oxygen,  to  which  Iodine  offers  but  two  par- 
allels, and  Bromine  but  one.  Finally,  Selenium  offers  one  com- 
pound, the  protoxide,  which  agrees  in  composition  with  hypo- 
delorous  acid  or  protoxide  of  Chlorine.  In  order  to  exhibit 
at  once  the  general  types  of  the  compounds  of  this  group* 
we  will  assume  the  letter  A  to  represent  any  member  of  the 
group  in  a  general  formula,  accenting  it  thus  A'  or  A"  when 
necessary  to  consider  or  represent  more  than  one  element  at 
the  same  time  and  in  the  same  formula.  Adopting  these  sym- 
bols then  we  may  construct  general  formulae  which  will  re- 
present the  types  of  all  known  combinations  of  the  members 
of  this  group  with  one  another,  and  these  types  we  find  to  be 
as  follows  : 


^4  CHEMICAL    CLASSIFICATION. 

AA'j—  AA}2—  AA'3—  AA'4—  AA'_—  AA'7— A2A'a- 

A2AV— A3A'5—  A4AV 
Corresponding  to  which  we  have 


S> 


AA'r 

-C10- 

-SeO- 

— TeCl— 

AA'2- 

-S02- 

-SeO 

2-Te03- 

-TeCl2- 

~C1S2~ 

-SCi2 

AA'a- 

-so,- 

-SeO 

3~Te03- 

-S02C1- 

^SOJ- 

-S02! 

AA'4- 

-C104. 

AA'5- 

-cio,. 

10.. 

B205-B 

2C16-IC1 

25. 

AA'7- 

-C107- 

-10, 

, 

A2A'2 

-s2o, 

2  ' 

A2A*5 

— s„o 

5.  or 

so2+so3 

1 

A3A'5' 

-s,o, 

j.  or 

S03  +  S03 

s? 

A4A'5- 

-S40; 

>  * 

We  have  already  alluded  to  the  number  and  characters  oi 
the  compounds  which  the  members  of  this  group  form  with 
those  of  other  groups,  and  this  portion  of  the  subject  will  also 
meet  with  further  consideration  in  speaking  of  the  other 
groups,  specially  and  individually. 

The  bodies  which  we  have  arranged  together  under  this 
first  class  compose  the  first  and  fifth  classes  of  Graham.  They 
are  collectively  termed  Basacigen  by  Dr.  Hare,  in  reference 
to  their  property  of  forming  both  acids  and  bases  by  uniting 
with  other  substances.  By  the  latter  chemist  also  this  group 
is  again,  in  deference  to  the  opinions  of  Berzelius,  subdivided 
into  two,  the  first  termed  Amphigen,  comprising  Oxygen,  Sul- 
phur, Selenium,  Tellurium ;  the  second  termed  Halogen,  com- 
prising Chlorine,  Iodine,  Bromine  and  Fluorine.  As  the  term 
Amphigen  has  not  come  into  very  general  use,  it  might  be 
well  to  substitute  it  for  the  term  Basacigen,  which  though 
very  expressive  in  itself  is  not  susceptible  of  etymological 
changes.  Should  it  be  thought  worth  while  to  subdivide  the 
whole  group  into  two  sub-groups,  then  for  the  same  reason 
that  Chlorine,  &c.  are  termed  Halogen,  Oxygen,  Sulphur,  &c. 
might  be  termed  Alkaligen,  as  has  indeed  been  proposed  by 
some  German  chemists.  Perhaps  the  best  nomenclature  after 
all  would  be  the  simplest,  viz  ;  to  associate  all  the  elements 
under  the  title  of  the  Oxy-Chlorine  Family, 


GROUP    IT.  25 

GROUP  II. 

The  second  group  comprises  Nitrogen,  Phosphorus,  Arsenic 
and  Antimony.  The  parallel  between  the  chemical  proper- 
ties and  relations  of  these  four  elements  is  for  the  most  part 
very  striking.  If  we  assume  the  letter  R  as  a  general  symbol 
for  the  whole  group,  while  A  represents,  as  before,  any  ele- 
ment belonging  to  group  1st,  we  shall  find  the  following  types 
for  the  compounds  of  the  two  groups.  RA — RA2 — RA2 — 
RA4 — -RA5?  corresponding  to  which  we  have 

to  RA— NO— PO 

to  RA2— N02—  AsS2— 

t0RA3—  NO3—NS3—  PO.—  PS3—  PCI3—  PBr3—  PF3— 
As03— Sb03— AsS3— SbS3— AsCl3— SbCl3+&c. 

to  RA4— N04— Sb04— SbS4— SbCl4. 

to  RA,— NO,— P0-— AsO,— Sb05  +  &c.  &c. 

In  addition  to  these,  phosphorus  forms  a  suboxide  to  which 
there  is  no  analogue  among  the  other  elements  of  the  2d 
group.  Besides  the  analogies  of  the  compounds  which  the 
members  of  this  group  form  with  those  of  group  1st,  there 
are  also  other  and  not  less  remarkable  relations.  Each  mem- 
ber of  group  2d  forms  with  hydrogen  a  gaseous  compound 
of  the  type  RH3.  These  compounds  are  severally  represented 
by  the  formulas  NH3,  PH3,  AsH3,  SbH3.  The  first  and  se- 
cond of  these  unite  with  the  halides  of  hydrogen  to  form  defi- 
nite compounds,  strongly  analogous  to  metallic  halides  and  of 
the  type  RH34-HA\  The  first  again,  ammonia,  is  capable 
also  of  uniting  with  the  oxides,  sulphides,  &c.  of  hydrogen 
to  form  powerful  oxybases  and  sulphobases,  which  moreover 
are  isomorphic  us  with  similarly  constituted  oxides  and  sul- 
phides of  potassium.  To  these  compounds,  the  phosphuret, 
arseniuret  and  antimoniuret  of  hydrogen  offer  no  parallels. 
Again,  ammonia  and  phosphuretted  hydrogen  are  capable  of 
forming  a  very  numerous  class  of  compounds  by  combining 
directly  with  oxides,  chlorides,  &c.  as  well  as  with  very  many 
classes  of  salts  composed  of  acids  and  bases.  Antimoniuret- 
ted  and  arseniuretted  hydrogen  appear  to  form  no  such  com- 

3 


26  CHEMICAL    CLASSIFICATION. 

pounds.  One  equivalent  of  the  hydrogen  of  ammonia  may 
be  replaced  by  an  equivalent  of  metal  forming  a  body  of  the 
type  NH2M,  and  presenting  characters  very  analogous  to  those 
of  a  protoxide  or  protochloride.  We  do  not  know  that  either 
of  the  compounds  of  the  other  three  members  of  this  group 
with  hydrogen  are  susceptible  of  a  similar  molecular  replace- 
ment. Lastly,  by  means  of  a  voltaic  current,  certain  of  the 
compounds  of  ammonia,  those  namely,  with  the  halides  of 
hydrogen,  may  be  decomposed,  the  ammonia  uniting  with  an 
equivalent  more  of  hydrogen  to  form  a  compound  metal  which 
forms  with  the  mercury  which  constitutes  the  negative  pole  of 
the  battery,  a  true  amalgam,  while  the  halogen  constituent  is 
given  off  at  the  positive  pole  of  the  circuit.  We  are  as  yet 
ignorant  whether  the  compounds  of  phosphuretted  hydrogen 
with  the  halides  of  hydrogen  are  or  are  not  capable  of  under- 
going a  similar  decomposition,  and  whether  or  not  there  may 
be  a  compound  of  phosphorus  and  hydrogen  exactly  analo- 
gous to  the  hypothetic  ammonium,  and  like  it  forming  an 
amalgam  with  mercury.  And  it  would  be  a  most  deeply  in- 
teresting experiment,  to  submit  to  electrolysis  in  contact  with 
mercury  the  compound  of  phosphuretted  hydrogen  and  iodo- 
hydric  or  bromohydric  acid,  represented  by  the  formula 
PH3-j-HI  or  PH3+HBr,  and  to  determine  whether  these 
compounds  are  not,  like  the  iodide  and  bromide  of  ammo- 
nium, in  all  chemical  relations,  true  iodides  and  bromides  and 
not  idohydrates  and  bromohydrates.  It  has  been  shown  by 
Rose  that  a  compound  of  phosphorus,  hydrogen  and  chlorine, 
exactly  analogous  to  sal-ammoniac,  exists  in  combination  with 
bichloride  of  titanium,  forming  a  lemon-yellow  substance, 
whose  formula  is  PH4Cl-f-3TiCl2.  The  combinations  of  the 
members  of  this  group  with  hydrogen,  illustrate  the  law  of 
grades  in  a  very  striking  manner,  those  chemical  properties 
and  relations  which  are  most  strongly  marked  in  the  nitrogen 
compounds,  shade  off  as  it  were  first  into  the  phosphurets, 
then  the  arseniurets,  and  finally  are  lost,  or  at  best  very  feebly 
exhibited  in  the  antimoniurets,  of  hydrogen.     In  the  com- 


GROUP   if,  27 

pounds  of  the  members  of  this  family  with  those  of  the  first 
group,  equally  striking  analogies  are  manifested.  For  exam- 
ple, the  nitric  and  antimonic  acids  N05  and  Sb05  unite  with 
but  one  equivalent  of  base,  phosphoric  acid  P05  unites  with 
one,  two,  or  three,  while  arsenic  acid  again  As05,  unites  with 
three  equivalents  of  base  alone.  For  the  formulas  of  the  tri- 
basic  salts  of  the  two  last  mentioned  acids,  we  have 
PO  5  +  Na02HO— PO  5  +  2NaO,HO— PO  -  +  3NaO, 
AsO  5  -f  Na0.2HO— AsO  5  +  2NaO.HO— AsO  5  +  3NaO, 
which  formulas  it  will  be  seen  are  mutually  convertible,  by 
the  simple  interchange  of  the  symbols  for  phosphorus  and 
arsenic.  Though  arsenic  acid  forms  but  one  class  of  salts, 
yet  the  type  of  the  three  classes  of  salts  formed  by  phospho- 
ric acid  is  not  lost  with  the  comp^11^/1'  f  nic,  but  dis- 
tinctly manifests  itself  in  th  :  we  have 
the  formulas  of  the  three  cIe  iz  :  the  mo- 
nobasic, the  bibasic  and  the                                     s  follow 

P05+NaO— P05 
corresponding  to  which  we 

AsS5+NaS— AsS5  f-  £NaS— AsS64-3Na 
formulas  which  are  mutually  convertible,  by  the  interchange 
of  symbols  for  oxygen  and  sulphur.  Here  again  the  law  of 
grades  is  beautifully  exhibited.  We  are  as  yet  unacquainted 
with  any  tribasic  sulpharseniate,  corresponding  to  the  tribasic 
arseniates  and  phosphates  whose  formulas  are  given  above, 
and  which  contain  both  a  stable  and  an  unstable  base.  It  is 
clear  that  should  such  compounds  ever  be  formed,  sulphides 
of  hydrogen  will  take  the  place  in  the  sulpharseniates  of  the 
oxide  of  hydrogen  in  the  oxyarseniates,  so  that  we  should 
have 

AsS  5  +  NaS.2HS— AsS  5  +  2NaS.HS— AsS  5  +  3NaS, 
corresponding  to 

AsO  5  +  Na0.2HO— AsO  5  +  2NaO.HO— AsO  5  +  3NaO. 
The  salts  formed  by  the  sulphides  of  nitrogen  and  phos- 
phorus have  not  yet  been  studied  and  are  well  worthy  of  at- 
tention.   The  nitric  and  antimonic  acids  as  already  observed 


28  CHEMICAL    CLASSIFICATION. 

unite  with  but  one  equivalent  of  base ;  on  the  other  hand 
however  it  appears  certain  that  the  sulphantimonic  acid  is  tri- 
basic,  the  formulae  of  several  of  its  salts  being  as  follows: 

SbS5  +  3BaS  +  6HO— SbS5,3Nas+18HO— $bS573AqS. 
which  obviously  correspond  with  the  tribasic  phosphates,  ar- 
seniates  and  sulpharseniates.  Still  further,  the  nitrous  and 
antimonious  acids  N03  and  Sb03  appear  to  unite  with  but 
one  equivalent  of  base  like  the  nitric  and  antimonic  acids. 
Phosphorous  and  arsenious  acids  on  the  other  hand  are  in  all 
probability  tribasic,  all  the  known  salts  of  the  former  acid 
being  constituted  upon  ^)he  formula  P03+3RO  while  those 
of  arsenious  acid  appear  to  come  under  the  formulae  As03  4- 
3RO,  As03+2RO,  As03+RO,  and  thus  to  be  monobasic 
and  bibasic  as  well  as  tribal:-  In  like  manner  the  formulae 
tlpfaarseni  e  an  exact  analogy  between 

i  and  the  art;  lae  of  the  two  classes  of  salts 

As03  +  (1,2.      .  >3  +  (l.  2.  3)RS.     Sulphar- 

senlous  acid  appears  gous  to  sulphantimonious 

acid  as  the  two  form  i  i  with  basic  sulphides  nu- 

merous native  salts  or  l  is  whose  formulae  are  precisely 

similar.  The  general  formulae  of  the  sulphantimonites  like 
those  of  the  sulpharseniates  may  be  expressed  bySbS3-f 
(1.2.  3)RS,  corresponding  to  which  we  have 

Zinkenite  SbS3  +  PbS— Feather  Ore  SbS3+2PbS— Boul- 
angerite  SbS3  +  3PS— Ruby  Silver  SbS3  +  3PbS. 

We  have  dwelt  upon  sulphur  salts  of  the  members  of  this 
group  at  considerable  length,  both  on  account  of  their  intrinsic 
interest,  and  because,  though  their  formulae  are  stated  in  many 
works  on  Chemistry,  no  deductions  whatever  appear  to  have 
been  drawn  from  them.  They  appear  to  us  to  illustrate  in  a 
very  striking  manner  the  law  of  grades,  and  to  point  out 
many  paths  of  research  upon  which  at  some  future  period  we 
hope  to  enter. 

Of  the  4  elements  which  compose  this  group,  two,  viz : 
arsenic  and  antimony  are  isomorphous  in  their  free  or  uncom- 
bined  state.    The  salts  of  phosphoric  and  arsenic  acids  which 


GROUP    II.  29 

are  similar  in  constitution  correspond  also  in  form.  No  cer- 
tain isomorphism  connects  the  compounds  of  hydrogen  with 
this  group,  while  on  the  other  hand  the  isomorphism  of  anti- 
mony and  arsenic  with  tellurium  preserves  a  resemblance  in 
this  respect  between  groups  first  and  second. 

Notwithstanding  the  isomorphism  of  arsenic  and  anti- 
mony, the  numbers  representing  their  atomic  volumes  do 
not  correspond,  the  number  for  antimony  being  according  to 
our  own  calculation  19.22  while  that  for  arsenic  is  12.68. 
Hence  there  must  be  some  exceptions  to  the  law  of  Dr.  Kopp. 
There  is  a  similar  disagreement  between  the  atomic  numbers 
of  the  two  substances,  the  number  for  antimony  being  .0519 
while  that  for  arsenic  is  .0792.*  Yet  it  seems  to  us  that  these 
apparent  discrepancies  rightly  considered,  will  entirely  disap- 
pear. Adopting  for  the  sake  of  simplicity  the  atomic  theory, 
we  reason  as  follows  :  arsenic  and  antimony  are  isomor- 
phous — the  volume  of  the  atom  of  arsenic  is  less  than  that 
of  antimony  in  the  proportion  of  12.68  to  19.22,  but  in  the 
same  bulk  a  crystal  of  arsenic  contains  more  atoms  of  ar- 
senic than  a  crystal  of  antimony  contains  atoms  of  antimony, 
in  the  proportion  of  .0792  to  .0519  ;  if  therefore  we  multiply, 
for  each  element,  the  volume  of  one  atom  by  the  number  of 
atoms  in  a  crystal  of  each,  is  it  not  perfectly  clear  that  we  ob- 
tain the  volume  or  bulk  of  all  the  matter,  arsenic  or  anti- 
mony, which  each  crystal  contains  ?  On  submitting  our  rea- 
soning to  the  rigid  test  of  calculation  we  actually  find  that  a 
crystal  of  antimony  and  an  equal  crystal  of  arsenic  contain  the 
same  volume  of  matter,  for  .0519  x  19.22  =  .997518  and.0792  x 
12.68  =  1.004256  the  difference  being  only  .006738,  a  coinci- 
dence which  must  be  regarded  as  very  remarkable,  when  we 
consider  the  unavoidable  errors  in  the  determinations  both  of 
the  specific  gravities  and  the  atomic  weights.  Still  further, 
we  have  said  that  tellurium  is  isomorphous  with  arsenic  and 
antimony  ;  now  the  atomic  volume  of  tellurium  is  .978  and 

*  The  sp.  gr.  of  water  is  here  taken  as  unity  and  not  as  before  1000. 

3* 


^0  CttEJNflCAL    CLASSIFICATION. 

its  atomic  number  10.22,  multiplying  these  two  together  we 
obtain  9.99516  which  is  almost  identical  with  the  numbers 
already  obtained  for  antimony  and  arsenic  !     Thus  we  have 

Arsenic     =  1.004256= unity  very  nearly. 

Antimony =.9  9  75 18   =  " 

Tellurium=. 999516   =  " 

Mean        =1.000430=  « 

We  might  perhaps  apply  to  the  numbers  thus  obtained,  viz  : 

by  multiplying  the  atomic  volumes  by  the  atomic  numbers, 

the  term  "crystalline  volumes."     Yet  it  will  be  immediately 

obvious,  from  a  consideration  of  the  manner  in  which  the 

atomic  numbers  and  the  atomic  volumes  are  obtained,  that 

their  product  must  always  be  unity,  since  if  W  represent  the 

atomic  weight  of  any  substance  and  S  its  specific  gravity,  we 

S 
shall  have  for  the  atomic  number  — ,  and  for  the  atomic  vol- 

W 

w  s    w   sw 

ume — ,  now  —  x  — = = !■  and  since  the  same  is  true  for 

s'        w    s    sw 

all  substances  whatever,  whether  simple  or  compound,  it  fol- 
lows that  the  crystalline  volumes  of  all  bodies  are  equal,  that 
is  to  say,  every  substance  whatever,  no  matter  what  may  be 
its  form  or  what  its  constitution,  contains  within  a  unit  of  vol- 
ume, one  cubic  inch  for  instance,  the  same  volume  of  ponder- 
able matter.  This  may  be  stated  otherwise  as  follows :  "  The 
volumes  of  the  atoms  of  all  substances  are  inversely  propor- 
tional to  the  number  of  atoms  which  are  contained  under  the 
same  surface."  This  law  may  be  made  of  great  use  in  the 
determination  of  the  atomic  weights  of  different  substances. 
Its  truth  appears  to  us  incontrovertible,  if  we  admit  the  truth 
of  the  premises.  The  members  of  group  2d  are  connected 
with  those  of  group  1  st,  as  already  observed  by  the  isomor- 
phism of  tellurium  with  arsenic  and  antimony.  In  addi- 
tion to  this,  however,  there  are  other  points  of  resemblance 
which  are  not  unworthy  of  notice.  Thus,  the  nitric,  phos- 
phoric, arsenic  and  antimonic  acids  are  analogous  in  constitu- 
tion to  the  iodic,  chloric  and  bromic  acids,  while  nitrous,  ar- 


GROUP    III.  31 

senious,  phosphorous  and  antimonious  acids  find  parallels  in 
sulphuric,  selenic  and  telluric  acids.  Hypo-nitric  and  hypo- 
antimonic  acids  again  are  analogous  in  type  to  chlorous  acid ; 
N04  and  Sb04  to  C104.  Antimonious  acid  moreover  resem- 
bles the  iodic  in  mode  of  combination  as  well  as  in  constitu- 
tion, thus  we  have  KO  4- Sb05  and  KO  +  2Sb05,  corresponding 
to  KO  +  10  5  and  KO  -f-2I05.  Arsenic  and  antimony,  the  former 
especially,  appear  sometimes  to  replace  sulphur  in  combination, 
and  to  act  the  part  of  basacigen  bodies.  Thus  we  have  FeS2  + 
FeAs— CoS2  +CoAs — NiS2  4-NiAs— Co2  As3 — FeAs— Ni2 
As — Mn2As — NiS24-NiSb — Ni2Sb  which  we  may  assimi- 
late to  FeS2  +  FeS  or  Fe2S3—  CoS2-f  CoS  or  Co2S3— NiS2  + 
NiS  or  Ni2S3 — Mn2S — Ni2S,  where  arsenic  and  antimony 
appear  to  be  substituted  for  an  equivalent  of  sulphur  in  the 
metallic  sesquisulphides. 

GROUP  III. 

The  third  group  comprises  also  four  elements.  They  are 
Hydrogen,  Zinc,  Cadmium  and  Magnesium,  which  collec- 
tively form  an  extremely  well  defined  natural  family.  The 
types  of  the  compounds  of  these  elements  with  the  members 
of  the  1st  or  basacigen  group  are  few  and  simple.  If  as  usual 
A  represents  a  member  of  group  1st,  and  R  any  element  be- 
longing to  the  group  now  under  consideration,  we  may  com- 
prehend all  the  combinations  of  the  members  of  the  two 
groups  under  the  general  formulas, 

R2A — RA — RA2,  corresponding  to  which  we  have  Zno0  ? 
— ZnO— Zn02— HO— HS— H02— HS2— CdO— MgO-ZnCl 
— HC1—  CdCl— MgCl,  &c.  &c. 

The  three  peramphides  or  rather  deut-amphides  of  this 
family,  viz  :  Zn02 — H02 — HS2  are  remarkable  for  the  insta- 
bility of  their  composition,  and  hence  it  is  not  very  probable 
that  we  shall  ever  obtain  higher  oxides,  sulphides,  &c.  All 
the  proto-amphides  of  the  members  of  this  group  are  on  the 
other  hand  remarkable  for  stability  and  form  very  powerful 
bases  which  enter  into  the  compositfon  of  a  great  number  and 
variety  of  salts.     The  similar  salts  of  the  protoxides  of  zinc, 


32  CHEMICAL    CLASSIFICATION* 

cadmium  and  magnesium  are  isomorphous.  Hydrogen  is  con- 
nected with  the  others  by  numerous  and  striking  analogies, 
though  it  enters  into  the  constitution  of  innumerable  substan- 
ces which  find  no  parallels  among  the  combinations  of  the 
other  members  of  the  group.  Recently,  indeed,  it  has  been 
shown  by  Dr.  Kane  that  hydrogen  is  to  be  regarded  as  a  metal, 
differing  from  other  metals  simply  in  physical  constitution,being 
at  ordinary  temperatures  a  gas,  in  the  same  manner  and  for  the 
same  reason  that  mercury  is  at  ordinary  temperatures  a  liquid. 
The  analogies  of  hydrogen  to  zinc,  are  strikingly  illustrated 
by  the  following  formulae  first  pointed  out  by  Dr.  Kane. 
ZnCl  +  6ZnO  HC1+6HO 

ZnCl+6ZnO  +  6HO  HC1  +  6HO  +  6HO 

ZnCl  +  6ZnO  +  10HO         HC1  +  6HO  +  10HO 
Again,   S03  +  ZnO  +  7HO  S03  +  ZnO  +  2HO,5ZnO 

S03-fZnO+4HO,3ZnO  S08  +  ZnO  +  7ZnO. 
The  equivalent  weights  of  the  members  of  this  group  are 
not  connected  by  any  simple  multiples,  in  other  words  they 
are  not  isomeric.  The  atomic  numbers  of  zinc  and  cadmium 
are  very  different,  that  of  the  former  being  21430,  that  of  the 
latter  15570.  Their  atomic  volumes  are  consequently  also 
different.  All  the  members  of  the  group  are  in  a  high  degree 
electropositive;  the  replacement  of  an  equivalent  of  hydro- 
gen by  an  equivalent  of  zinc  being  the  method  universally 
employed  to  generate  voltaic  currents.  This  group  is  not  con- 
nected with  the  second  by  any  definite  links,  in  the  present 
state  of  our  knowledge,  and  its  relations  to  group  1st  are  de- 
pendant chiefly  upon  its  intimate  connexion  with  the  next 
family,  with  which  indeed  it  is  associated  both  by  Graham 
and  by  Kane, 

GROUP  IV. 

Group  4th  comprises  Iron,  Manganese,  Chromium,  Cobalt 
and  Nickel.  The  members  of  this  group,  like  those  of  the 
last,  constitute  an  extremely  well  defined  natural  family.  The 
types  of  their  combinations  with  the  members  of  group  1st 
are  numerous,  and  it  is  in  this  respect  that  they  differ  from 


GROUP    IV. 


33 


the  elements  constituting  group  3d,  with  which,  as  already  ob- 
served, their  connection  is  very  intimate.     These  types  are  as 
follows : 
R2A— RA— RA2— RA3— R2A3--R2A7— R2A5— R3A4 

Corresponding  to  which  we  have 
MnO.    Mn2S-MnO-Mn02-Mn0  3-Mn203-Mn207-Mn205-Mn304 
FeO.  1       FeO— FeS2—  Fe03—  Fe203—        1  1  Fe304 

CrO.  1        CrO—     1  Cr03— Cr203  —        ?  1  1 

CoO.  1       CoO— C1S2  1        Co203—        1  1  Co304 

NiO.     Ni2S-NiO— NiS2  ?        Ni203—        1  1  1 

In  their  general  chemical  relations  the  five  members  of  this 
group  very  strongly  resemble  each  other.  They  all  form 
protoxides  which  are  powerful  bases  and  the  similar  salts  of 
which  are  isomorphous.  The  most  interesting  of  these  salts 
is  a  class  of  sulphates  constituted  according  to  the  general 
formulae 

RO  +  S03  +  HO  +  6aq 
isomorphous,  and  capable  of  forming  double  salts  with  the 
sulphates  of  soda  and  potassa,  in  which  one  equivalent  of 
either  of  these  last  replaces  the  one  equivalent  of  constitu- 
tional water  in  the  original  salt.  The  sesquioxides  of  the 
members  of  this  group  form  also  by  uniting  with  acids,  sev- 
eral very  remarkable  series  of  compounds,  which  like  the  salts 
of  the  protoxides  are  isomorphous.  Chromium,  manganese 
and  iron  form  acids  by  uniting  with  three  equivalents  of  oxy- 
gen. Of  these  the  chromic  acid  is  the  most  stable,  the  man- 
ganic acid  less  so,  the  ferric  acid  is  decomposed  by  the  slight- 
est causes.  The  other  two  elements,  cobalt  and  nickel,  do  not 
form  acids  at  all,  so  far  at  least  as  we  at  present  know.  Here 
the  law  of  grades  is  distinctly  shown.  Manganese  again 
forms  two  distinct  acids  with  oxygen,  to  which  the  other  mem- 
bers of  the  group  offer  no  parallel.  The  number  of  com- 
pounds formed  by  manganese  is  moreover  greater  than  the 
number  of  those  formed  by  any  one  of  the  other  members  of 
the  group.  For  these  reasons  we  place  manganese  at  the 
head  of  the  group,  and  may  without  impropriety  give  its  name- 
to  the  whole  family.  The  members  of  this  group  unite  with 
cyanogen  to  form  a  remarkable  series  of  compounds,  which 


34  CHEMICAL    CLASSIFICATION. 

by  their  union  as  cyan-acids  with  cyano-bases,  form  a  series 
of  salts,  the  elements  of  which  are  united  by  most  powerful 
affinities.  Of  these  cyano-salts  there  are  two  classes ;  in  the 
first  class,  a  protocyanide  of  a  metal  of  group  four,  acts  as  an 
acid  towards  the  cyanides  of  other  radicals ;  in  the  second 
class  of  salts  a  sesquicyanide  of  a  metal  belonging  to  group 
four,  acts  as  an  acid  towards  the  cyanides  of  other  radicals  or 
of  other  metals  belonging  to  the  same  group.  Belonging  to  the 
first  of  these  classes  of  salts  we  have  but  one  series,  viz :  the 
cyano-ferrites  represented  by  the  general  formula 
Fefcy+2MCy. 

The  second  class  of  salts  is  more  numerous  and  is  repre- 
sented by  the  formula 

R2Cy3+3MCy. 

Corresponding  to  which  we  have 
Fe2Cy3+3KCy,Mn2Cy3+3KCy,Cr2Cy3+3KCy,Co2Cy3 
-f  3KCy,  Ni2Cy3  +3KCy,  (?) 

The  members  of  this  group  are  connected  with  those  of  group 
1st,  by  several  distinct  and  well  ascertained  isomorphisms.  Thus 
the  chromic  and  manganic  acids  form  salts  which  are  isomor- 
phous  with  the  corresponding  sulphates  and  seleniates.  The 
chromates  moreover  resembles  the  sulphates  in  solubility  and 
in  their  mode  of  forming  double  salts.  Again,  a  peculiar  acid 
of  manganese  has  occasionally  been  obtained  in  combination 
with  potassa,  forming  a  salt,  the  formula  of  which  is  Mn20s 
4-KO,  and  which  is  isomorphous  wtth  chlorate  of  potassa 
C1CL+KO.  Still  farther,  the  salts  of  hypermanganic  acid 
are  isomorphous  with  the  corresponding  salts  of  hyperchloric 
acid  Mn207  +  R0  with  C107  +  R0.  Hence  it  is  clear  that,  in 
combination  at  least,  two  equivalents  of  manganese  replace  and 
are  isomorphous  with  one  equivalent  of  chlorine.  And  thus 
group  1st  and  4th  are  connected  by  a  two-fold  isomorphism. 
We  may  here  observe  that  as  one  equivalent  of  manganese 
is  in  combination  isomorphous  with  one  equivalent  of  sulphur, 
two  equivalents  of  manganese  ought  to  be  isomorphous  with 
two  equivalents  of  sulphur,  consequently  the  salts  of  manga- 
nese of  the  type  Mn205  +  RO,  which  from  analogy  we  will 


GROtJ?   V,  35 

call  hypomanganates,  should  be  found  isomorphous  with  the 
hyposulphates,  S205  +  RO,  and  the  hyposulphates  should 
therefore  be  isomorphous  with  the  chlorates.  We  have  no- 
ticed this  point  because  the  attention  of  chemists  does  not 
seem  to  have  been  directed  towards  it,  obvious  as  it  may  ap- 
pear. The  salts  of  the  protoxides  of  this  group  are  isomor- 
phous with  the  similar  salts  of  the  protoxides  of  group  3d, 
and  there  is  furthermore  a  very  great  analogy  in  other  respects 
between  the  salts  of  the  two  series  of  oxides.  All  the  metals 
of  group  4th  dissolve  in  hydrated  acids  by  a  simple  replace- 
ment of  hydrogen,  and  the  three  types  of  the  compounds  of 
group  3d  correspond  to  the  first  three  types  of  the  compounds 
of  group  4th,  with  the  basacigen  family. 

The  metals  composing  this  group  possess  nearly  the  same 
atomic  weights  and  specific  gravities,  and  further  researches 
may  perhaps  identify  them  in  these  respects.  The  specific 
gravity  of  chromium  however  differs  greatly  from  the  mean 
specific  gravity  of  the  other  four  metals.  The  mean  of  the 
atomic  members  of  iron,  cobalt,  manganese  and  nickel,  is 

.2896,  and  the  mean  atomic  volume  is  consequently  ■ or 

.2896 

3.4530.  It  is  worthy  of  notice  that  the  molecules  pi  these 
four  metals  are  smaller  than  those  of  any  other  simple  sub- 
stance with  which  we  are  acquainted. 

Finally,  iron  and  nickel  are  the  only  two  substances  which 
are  certainly  known  to  be  susceptible  of  magnetism,  though 
cobalt  and  manganese  have  been  supposed  to  share  this  pro- 
perty also ;  the  equivalents  of  the  two  former  we  may  also 
remark  have  the  same  specific  heat. 

GROUP  V. 

The  fifth  group  comprises  Aluminum,  Glucinum  and  Zirco- 
nium. These  three  elements  are  nearly  related  to  those  of 
group  four,  and  are  classed  with  them  by  Graham  and  by- 
Kane.  They  differ  however  essentially  from  them  in  forming 
but  a  single  molecular  type  by  combining  with  the  members 
of  group  1st.     This  type  is  represented  by  the  formulge  R2  A  3 . 


35  CHEMICAL  CLASSIFICATION, 

The  sesquioxides,  alumina,  glucina  and  zirconia,  are  capable 
of  acting  the  part  of  acids  toward  metallic  protoxides  as  well 
as  of  powerful  bases  toward  the  strong  acids.  The  salts  of  alu- 
mina and  glucina  are  probably  isomorphous  with  those  of 
zirconia,  though  this  point  has  not  yet  been  satisfactorily  as- 
certained, they  are  however  certainly  isomorphous  with  the 
sesquioxides  of  the  members  of  group  four,  both  in  a  free  state 
and  in  a  state  of  combination,  Alumina  frequently  replaces 
the  sesquioxides  of  iron  in  mineral  compounds  as  well  as  in 
artificially  prepared  salts.  ^-As  an  instance  of  the  striking 
analogy  between  the  chemical  relations  of  the  sesquioxides 
of  groups  four  and  five  we  may  cite  the  general  formulae  of 
the  alum  family. 

R'0,S03+R203,3S03-{-2dag, 
corresponding  to  which  we  have  the  alumina,  iron,  manga- 
nese and  chrome-alums.  In  like  manner  we  have  a  class  of 
double  oxalates,  the  general  formulae  of  which  is 
3(R'0,C203)  +  R203.3C203+6ag, 
corresponding  to  which  we  have  double  oxalates  of  chro- 
mium, aluminum,  and  iron  with  oxalates  of  potassa,  which  are 
like  the  alums  isomorphous.  The  elements  which  we  have 
arranged  under  group  5th  are  connected  with  the  basacigen 
family,  and  with  the  members  of  group  3d,  indirectly  by  their 
relation  with  group  4th.  The  three  last  groups,  viz :  groups 
3d,  4th,  and  5th,  constitute  in  a  great  measure  the  2d  or  mag- 
nesian  class  of  Graham.  They  are,  as  we  have  already  stated, 
very  intimately  connected,  as  well  by  chemical  as  by  physi- 
cal properties,  though  we  have  thought  it  more  in  accordance 
with  the  true  principles  of  a  natural  classification,  to  arrange 
them  under  three  separate  classes  or  groups.  As  an  illustra- 
tion of  their  capacity  of  replacing  one  another  in  combination, 
we  cite  the  following  formulae  derived  for  the  most  part  from 
the  mineral  kingdom. 

Fe0  +  Fe203.     Zu0  +  Al203.     MnO-fMn203. 

FeO  +  Cr203.     MqO  +  Al203.     Zuo  +  Mn2Os. 
We  may  remark  in  conclusion  that  aluminum  is  isomeric 
with  iron  and  manganese  13.72  x  2=27.44,  and  that  the  equiv- 


alent  Of  glucinum  so  nearly  approaches  that  of  the  other  mem- 
bers of  the  two  groups,  viz :  the  4th  and  5th,  that  we  may 
reasonably  expect  that  upon  more  accurate  investigation,  it 
will  be  found  isomeric  with  them.  The  equivalent  of  zirco- 
nium is  however  entirely  removed  from  the  series  and  approx- 
imates toward  that  of  zinc. 

GROUP  VI. 
The  sixth  group  comprises  four  elements,  Molybdenum, 
Tungsten,  Vanadium,  Columbium.     The  compounds  of  these 
elements  with  the  members  of  group  1st  may  be  arranged  un- 
der three  types.  • 

RA— RA2— RA3 
corresponding  to  which  we  have 

MoO--Mo02—  Mo03 
?         TnQ2—  Tn03 
VO— VO,-V03 
?      W02-W0s 
It  will  be  immediately  observed  that  these  types  are,  so  far 
as  they  extend,  precisely  similar  to  those  of  group  4th.     Sev- 
eral' of  the  salts  of  tungstic  and  molybdic  acids  are  isomor- 
phous,  while  on  the  other  hand,  one  of  the  forms  of  chromate 
of  lead  corresponds  with  that  of  the  molybdate  of  the  same 
base.     Between  the  vanadic  and  chromic  acids  there  is  also 
considerable  resemblance,  though  their  compounds  are  not 
known  to  be  isomorphous.    There  exist,  moreover,  compounds 
of  Molybdenum  and  Tungsten  with  oxygen  and  chlorine,  pre- 
cisely analogous  in  composition  to  the  so-called  chloro-sulphu- 
ric  and  chloro-chromic  acids,  thus  we  have 
2Cr03+CrCl3  or  Cr02,CL 
2S03+SC13  or      S02,C1. 
2Mo03  +MoCl8*or  Mo02,Cl. 
2WO   4-WCI3  or      W02CI. 
Formulae,  which  together  with  the   analogies  which  we  have 
already  mentioned,  connect  this  group  very  evidently  with 
the  4th,  and  indirectly  with  the  1st,  3d,  and  5th  groups.     The 
protoxides  of  Vanadium  and  Molybdenum  are  not  powerful 

4 


38  CHEMICAL    CLASSIFICATION. 

bases  like  those  of  group  4th,  neither  do  the  four  metals  com- 
posing this  group  form  with  the  basacigen  family  sesqui-com- 
pounds  as  do  all  the  members  of  group  four.  Molybdenum 
forms  with  sulphur  a  higher  acid  than  the  sulpho-molybdic, 
the  formulae  being  MoS4,  and  thus  apparently  connects  this 
group  with  group  2d ;  the  compounds  of  this  acid  with  sul- 
phur-bases are  well  worthy  of  attention,  only  one  compound,, 
the  potassium-salt  MoS4  +  KS,  being  at  present  known.  The 
chemical  properties  and^rejations  of  the  four  elements  which 
we  have  associated  together  as  group  6th  are  in  general  very 
similar,  though  further  researches  are  wanting  to  enable  us  to 
assign  with  certainty  the  proper  position  of  columbium. 

Both  the  atomic  weight  and  the  specific  gravity  of  Tung- 
sten are  very  nearly  double  those  of  molybdenum,  thus, 
2Mo=95.92=W=94.8  nearly,  and  S.GW=17.22=2S.GMo 
=  17.23.  The  atomic  numbers  or  chemical  densities  are  con- 
sequently the  same  for  both  metals,  and  they  likewise  agree 
in  atomic  volume,  or  in  the  size  of  their  molecules.  The  mean 
atomic  number  is  .1811,  and  the  mean  atomic  volume  5.52. 
The  specific  gravities  of  vanadium  and  columbium  are  as 
yet  unknown. 

GROUP  VII. 

Group  7th  comprises  Copper,  Mercury,  Bismuth,  and  Pal- 
ladium. The  types  of  the  compounds  formed  by  the  mem- 
bers of  this  group  with  those  of  group  1st  are  three  in  num- 
ber. 

R2A— RA— RA2, 
corresponding  to  which  we  have 

Cuo0— CuO— Cn02 

Hg~20— HgO—  ? 

Bi20?— BiO— Bi02 

Pd20— Pd0—Pd02 
In  their  general  relations  the  four  metals  composing  group 
7th,  agree  in  a  remarkable  manner,  though  there  exist  between 
their  compounds  no  observed  isomorphisms.     Their  corres- 
ponding oxides  are  all  insoluble  in  water ;  the  suboxides  of 


group  vii.  39 

copper,  mercury  and  palladium  forming  definite  and  exceed- 
ingly well  marked  salts  with  acids,  a  property,  it  may  be  re- 
marked, which  is  rare  in  oxides  of  that  constitution.     The 
protoxides  of  each  is  in  like  manner  a  powerful  base,  while 
the  pertoxides  of  copper,  bismuth  and  palladium  are  analo- 
gous in  instability  and  in  incapacity  to  form  well  denned  com- 
pounds with  either  acids  or  bases.     The  protoxides  of  cop- 
per, bismuth  and  mercury  exhibit   moreover  a  remarkable 
tendency  to  form  compounds  containing  an  excess  of  base. 
The    subnitrates  of  copper  and  bismuth  are  analogous  in 
composition,  according  to  Graham,  being — N05,HO-i-3CuO 
and  NO§,HO  +  3BiO  ;  their  subsulphates  also  agree  in  compo- 
sition if  we  omit  basic  water,  thus,  S03+3CuO  and  S03  + 
3BiO.     Group   7th  is  connected  with  groups  3d  and  4th  by 
the  isomorphism  of  the  double  sulphate  of  copper  and  po- 
tassa  with  the  corresponding  double  sulphates  of  zinc  and 
potassa,  and  of  iron  and  potassa,  thus  we  have  CuO,S03  + 
KO,S03+6aq  isomorphous   with   ZnO,S03+KO,S03-f  6aq 
and  FeO,S03  +KO,S03  +6aq.     The  double  cyanide  of  mer- 
cury and  potassium  is  moreover  isomorphous  with  the  double 
cyanide  of  zinc  and  potassium  HgCy-fKCy  with  ZnCy  + 
KCy,  both  these  salts  appearing  in  octohedrons  of  the  regular 
system.     Bismuth  is  associated  with  the  2d  or  nitrogen  group 
by  Dr.  Kane,  on  the  ground  of  the  isomorphism  of  its  sulphide 
with  the  tersulphide  of  Antimony,  yet  as  its  oxides  do  not 
form  well  defined  salts  with  alkaline  bases,  and  as  it  does  not 
form  with  hydrogen  the  characteristic  gaseous  compound  of 
the  type  RH3,  we  cannot  admit  the  propriety  of  displacing  it 
from  its  original  position. 

No  isomerism  exists  between  the  equivalents  of  the  four  el- 
ements composing  this  group,  nor  are  their  atomic  numbers 
and  atomic  volumes  connected  by  any  very  certain  and  defi- 
nite relations.  The  atomic  numbers  of  the  four  metals  are 
as  follows:  Copper=.2742,  Mercury  .1321,  Bismuth  .0922, 
Palladium  .2153,  taking  the  number  for  Copper  as  unity,  the 
number  for  the  other  metals  will  be  to  it  nearly  in  the  follow- 


49  CHEMICAL    CLASSIFICATION 

ing  ratios,  mercury  |,  bismuth  J,  palladium  J,  and  the  atomic 
volumes  will  of  course  be  in  the  inverse  ratio,  viz  :  copper  1, 
mercury  2,  bismuth  3,  palladium  If. 

GROUP  VIIL 

The  8th  group  of  our  classification  comprises  5  elements, 
viz:  Barium,  Strontium,  Calcium,  Lead  and  Silver.  The 
types  of  the  compounds  of  the  members  of  this  group  with 
the  members  of  group  ls^are  three  in  number. 

R5A— RA— RA2, 
corresponding  to  which  we  have 

Ag,0— AgO— Ag02 
Pb20— PbO— Pb02. 


?  _BaO— Ba0; 
?  _SrO— Sr02.' 
?     _CaO— CaO 


2' 

The  similarly  constituted  salts  of  barium,  strontium  and  lead 
are  isomorphous  and  agree  remarkably  in  solubility  in  water 
and  in  their  purely  chemical  relations.  Thus  the  sulphates  of 
these  three  elements  occur  in  nature  crystallized  in  the  same 
form,  and  when  artificially  prepared  agree  in  their  insolubility 
in  appearance,  and  in  their  chemical  properties.  In  like  man- 
ner the  nitrates  of  lead,  barium  and  strontium  are  isomor- 
phous and  similarly  constituted.  Calcium  is  connected  with 
the  other  members  of  this  group,  by  the  isomorphism  of  one  of 
the  forms  of  its  carbonate,  viz  :  arragonite,  with  the  carbonates 
of  baryta  and  strontia,  by  the  insolubility  of  its  sulphate,  and 
by  a  general  similarity  in  chemical  relations.  We  may  also 
add,  that  agreeably  to  the  researches  of  Newmann,  the  speci- 
fic heats  of  the  equivalents  of  the  Carbonates  of  Lime,  Baryta? 
strontia  and  lead  are  the  same,  and  that  the  same  relation 
of  equality  holds  good  for  the  specific  heats  of  the  sulphates 
of  the  same  basis.  Silver  was  first  classed  with  lead  by  Dr° 
Kane,  and  the  two  metals  agree  very  closely  in  chemical  pro- 
perties, in  the  insolubility  of  their  chlorides,  bromides  and 
iodides,  &c,  but  their  salts  are  not  connected  by  any  known 
isomorphisms.     On  the  whole  then  we  may  regard  this  group 


GROUP    IX.  41 

as  being  extremely  well  defined  and  as  presenting  a  fair  ex- 
ample of  a  Natural  family  in  Chemistry.  With  groups  3d  and 
4th  this  family  is  connected  by  the  isomorphisms  of  the  carbon- 
ates of  strontia  and  baryta,  with  one  of  the  forms  of  the  carbon- 
ates of  magnesia  and  of  iron,  by  the  isomorphism  of  the  ordinary 
carbonate  of  lime  or  Iceland  spar  with  the  usual  forms  of  the 
carbonates  of  iron  and  magnesia,  and  by  the  analogy  in  con- 
stitution and  in  form  of  sulphates  of  iron  and  of  lime  whose 
formulae  are  S03  +  FeO  +  2HQ  andCaO  +  S03  +2HO.  The 
relations  between  this  group  and  group  1st  are  in  the  present 
state  of  our  knowledge  indirect,  being  traced  chiefly  through 
groups  3d  and  4th. 

No  isomerisms  subsist  between  the  equivalents  of  the  ele- 
ments constituting  this  group.  The  atomic  numbers  and 
atomic  volumes  of  silver  and  of  lead,  the  only  members  of  the 
group  for  which  they  can  at  present  be  determined,  are  also 
unconnected  by  any  simple  ratios.  The  specific  heat  of  the 
atom  of  silver  is  double  that  of  lead,  and  the  former  metal  is 
apparently  more  highly  electro-negative  than  the  latter. 

GROUP  IX. 

Group  9th  comprises  Platinum,  Titanium,  Iridium  and 
Osmium.  The  complete  series  of  the  compounds  formed  by 
the  members  of  this  group  with  those  of  group  1st  are  5  in 
number,  viz  : 

RA— RA2— RA3— RA4— R2A3, 
corresponding  to  which  we  have 

PtCl— PtCl2— ?    —    ?    —    ? 

TiO— TiCla—  ?    —    ?     —    ? 

IrO— IrCl2— Ir03—   ?     —  Ir0Cl, 

OsCl— 0sCl2— OsCl3— 0s04— 0s2CL. 
The  four  elements  which  we  have  arranged  under  group 
9th,  correspond  for  the  most  part  very  closely  in  chemical  pro- 
perties and  relations.  The  bichlorides  of  all  these  metals  form 
with  chloride  of  potassium,  highly  characteristic  chloro-salts 
which    crystallize   in   regular  octahedrons.      Their    general 


42  CHEMICAL  CLASSIFICATION. 

formula  is  RCU+KC1.  The  corresponding  compounds  of 
platinum,  iridium  and  osmium  are  all  isomorphous.  None 
of  the  protoxides  of  this  group  are  very  powerful  bases  and 
their  binoxides  like  compounds  of  that  type  generally,  are  ca- 
pable of  uniting  to  a  certain  extent  with  both  acids  and  bases. 

With  the  7th,  or  copper  family,  this  group  is  connected  by 
the  isomorphism  of  the  corresponding  salts  of  the  chloropallad- 
ious,  and  chloropalladic^acids  with  the  chloroplatinous  and 
chloroplatinic  acids. 

With  group  2d  this  group  is  connected  by  the  analogy  in 
composition  of  osmic  acid  with  hypo-nitric  and  hypo-anti- 
monic  acids.  With  group  4th  this  group  may  possibly  be 
connected  by  the  analogy  of  the  sesquichlorides  of  iridium 
and  osmium  to  the  sesquichlorides  of  iron  and  manganese. 

Of  the  four  metals  composing  this  group  platinum  and  iri- 
dium are  certainly  isomeric,  the  equivalent  of  each  being  98.84. 
The  equivalent  of  osmium,  viz  :  99.72,  nearly  approaches  that 
of  platinum  and  iridium  as  to  lead  to  the  suspicion  that  more 
accurate  researches  will  establish  their  identity.  Finally  the 
equivalent  of  Titanium  as  at  present  received  is  almost  exact- 
ly one-fourth  of  the  equivalent  of  Platinum  and  Iridium — 24.5 
X4=98.00. 

The  atomic  numbers  of  platinum,  iridium,  and  titanium 
are  also  equal,  the  mean  being  .2179;  the  atomic  volumes 
consequently  also  correspond,  being  for  each  4.59.  The  spe- 
cific gravity  of  osmium  is  stated  by  Graham  as  being  "  about 
10,"  in  this  case  its  atomic  volume  will  be  nearly  twice  and 
its  atomic  number  nearly  one-half  the  atomic  volumes  and 
atomic  numbers  of  the  other  metals  composing  group  9th. 

GROUP  X. 

Group  10th  comprises  Gold,  Uranium,  Rhodium  and  Tin. 
The  types  of  the  compounds  formed  by  the  members  of  this 
group  with  the  first  or  basacigen  family  are  four  in  number, 
viz :  R2  A — RA— RA2— R2  A3  corresponding  to  which  we  have 
Au20,  Au203,  UO— U,63—  R203—  SnO— Sn02— Sn30,.  ' 


group  x.  43 

The  sesquioxides  of  all  these  metals  agree  in  being  feebly  acid 
and  basic;  that  of  tin  has  as  yet  been  but  imperfectly  examined. 
The  sesquichlorides  of  gold,  uranium  and  rhodium,  form 
well  characterized  chloro-salts  with  the  chlorides  of  the  alka- 
line metals.  This  group  is  connected  with  the  last  by  the 
isomorphism  of  the  chlorostannates  and  chloroplatinates  of 
potassium,  SnCl2  +  KC1  and  PtCl2  +KC1 ;  by  the  isomorphism 
of  the  native  dentoxides  of  tin  and  titanium,  Sn02  and  Ti02, 
and  by  the  analogy  of  the  sesquichlorides  of  gold,  uranium 
and  rhodium,  with  those  of  osmium  and  iridium. 

Between  the  elements  composing  this  group  no  probable 
isomerism  exists,  though  the  atomic  weight  of  gold,  as  stated 
by  Graham,  is  nearly  identical  with  that  of  osmium,  as  at  pre* 
sent  received.  The  atomic  number  of  gold  is  identical  with 
that  of  silver,  with  which  metal  gold  is  isomorphous  in  the 
metallic  state  ;  but  the  analogy  between  the  two  metals  ceases 
here. 

The  atomic  number  of  rhodium  closely  approximates  to 
that  which  we  have  stated  for  the  last  group,  with  which 
therefore  it  is  in  this  way  connected.  The  atomic  number 
of  uranium  is  remarkable  as  being  very  small,  viz  :  .0414 ;  its 
atomic  volume  is  consequently  larger  than  that  of  any  metal 
yet  described,  viz  :  24.15. 

Finally  the  specific  heats  of  the  equivalents  of  gold  and 
tin  agree  with  each  other  and  with  that  of  platinum. 

GROUP  XI. 

The  eleventh  group  of  our  classification  comprises  Potas- 
sium, Sodium,  and  Lithium,  commonly  known  as  the  alkaline 
metals.  These  3  elements  are  connected  together  by  very 
strong  analogies  in  their  chemical  properties  and  relations,  but 
not  by  any  well  established  isomorphisms.  Their  isomor- 
phism in  the  metallic  state  appears  tolerably  certain.  The  most 
energetic  affinities  are  exerted  by  the  protoxides  of  these 
metals ;  the  greater  number  of  the  salts  which  they  form  with 
oxy-acids  are  soluble  in  water  and  neutral  in  composition, 


44  CHEMICAL    CLASSIFICATION. 

and  their  relations  to  other  oxides  are  almost  invariably  those 
of  bases  to  acids.  With  group  8th  they  are  connected  by  the 
isomorphism  of  the  sulphate  of  soda  with  sulphate  of  silver. 
Under  certain  circumstances  an  equivalent  of  potash  or  soda 
may  be  replaced  in  combination  by  an  equivalent  of  Lime-f 
an  equivalent  of  waj^r,  or  CaO  +  HO,  and  thus  this  group  is 
connected  with  group  8th  and  4th  at  the  same  time.  Again 
we  find  that  one  equivalent  of  nitrogen  +  four  equivalents  of 
hydrogen  are  capable  of  replacing  potassium  in  combination 
without  change  of  form,  NH4  being  isomorphous  with  K,  and 
thus  this  group  is  connected  with  Groups  2d  and  3d. 

No  isomerism  appears  to  subsist  between  the  equivalents  of 
the  members  of  this  group.  The  atomic  number  of  potassium 
is  very  nearly  double  that  of  sodium,  and  its  atomic  volume  is 
consequently  one  half  that  of  the  latter  metal.  The  specific 
gravity  of  lithium  appears  not  to  have  been  determined,  its 
atomic  weight  is  very  remarkable  as  being  lower  than  that 
of  any  other  metal,  unless  indeed  hydrogen  be  regarded  as 
such. 

GROUP  XII. 

The  twelfth  group  comprises  2  elements— Yttrium  and 
Thorium.  The  compounds  of  these  two  metals  are  as  yet 
very  imperfectly  known.  Their  oxides  are  regarded  as  pro- 
toxides, and  bear  considerable  analogy  to  each  other  in  chemi- 
cal properties  and  relations.  No  definite  relations  have  been 
established  between  them  and  the  members  of  any  other  group. 

GROUP  XIII. 
Group  13th  comprises  Cerium,  Lantanium,  Didymium,  Er- 
bium and  Terbium.  Our  knowledge  of  these  substances  is  as 
yet  too  much  imperfect  to  admit  of  our  entering  into  their  rela- 
tions and  properties,  sufficiently  to  establish  their  position  in 
the  same  class.  They  all  occur  in  nature  in  the  same  minerals 
and  are  exceedingly  difficult  to  separate  from  one  another, 
by  chemical  means.     The  last  four  in  the  order  which  we 


GROUP    XIV.  45 

have  mentioned,  have  been  discovered  by  Mosander  within  a 
few  years,  and  are  yet  under  his  investigation. 

GROUP  XIV. 

Group  14th  comprises  Carbon,  Boron  and  Silicon.  These 
elements  are  associated  together  by  Graham  upon  the  ground 
that  they  exhibit  a  general  resemblance  to  one  another  with- 
out any  precise  relations.  Independently,  however,  of  the 
non-agreement  of  the  types  of  their  compounds  with  the  basa- 
cigen  group,  carbon  enters  into  the  constitution  of  an  immense 
number  and  variety  of  compounds,  to  which  boron  and  silicon 
offer  no  parallels.  If  however  we  reduce  the  received  equiv- 
alents of  boron  and  silicon  by  one-third,  as  proposed  in  the 
case  of  silicon  by  Dr.  Clarke,  the  silicic  and  boric  acids  be- 
come analogous  in  constitution  to  carbonic  acid,  S0o  and  BO., 
to  C02.  This  view  of  the  constitution  of  the  two  former  acids 
is  supported  by  their  general  analogy  to  carbonic  acid  in 
chemical  relations,  they  are  feeble  acids,  and  are  at  the  same 
time  capable  of  entering  into  combination  with  bases  in  many 
proportions.  Moreover,  the  formulae  of  the  compounds  of 
boron  and  silicon  generally,  become  much  more  simple  by 
making  the  proposed  change,  than  they  are  at  present,  as  will 
readily  be  seen  from  a  comparison  of  the  following  formulae, 
which  we  have  calculated  for  the  purpose. 

Old  View. 

.      2SiF3+3KFl, 

2BF3+3KF1, 

3NaO  +  2B03, 

Biborate  of  Soda  Borax.    NaO  -f  2BO  3 , 

NaO+  B03, 
Boracite.  3MgO  +  4BO  g , 

Picrosmine.  3MgO  +  2SiO  3 , 

Pyroxene.  3MgO,2SiO  3  +  3CaO,2SiO , 

Steatite.  3MgO,2Si03  +  Al2032Si086HO 

Amphigen  or  Analcime.  3RO,2SI03  +  3(Al20352Sio3)±aq 
Felspar,  Albite,  Stilbite.   RO;Si03  +  A)a033Si03  ±aq. 


46  chemical  classification. 

New  View. 
SiF2  +  KF,  (Clark.) 
BF2  +  KF, 
Na0+B02 
Biborate  of  Soda  Borax.    NaO  +  3B02 

^    2NaO+3B02  like2NaO  +  3C02. 
Boracite.  MgO-f2B02 

Picrosmine.  M  gO  +  SiO  2 

Pyroxene.  MgO,Si02  +  CaO,Si02  like  MgO, 

C02  +CaO,C02.     Dolomite. 
Steatite.  Mg0,Si02+Al203,3Si02+6H0 

Amphigen  or  Analcime.  R0,Si02  +  2(Al203,3Si02)±aq 
Felspar,  Albite,  Stillite.      R0,3Si02  +  Al2~033Si02~ 

The  formulae  of  other  borates  and  silicates  are  not  however 
always  rendered  more  simple  by  the  proposed  change  in  the 
equivalents  of  boron  and  silicon,  so  that  the  expediency  of 
such  a  change  must  remain  for  the  present  undecided,  and  we 
must  admit,  that,  as  in  the  case  of  the  last  group,  further  re- 
searches are  wanting,  before  we  can  assign  with  any  degree 
of  probability,  the  proper  places  of  the  elements,  carbon,  boron 
and  silicon. 


Thus  far  then  we  have  endeavoured  to  display  the  analo- 
gies which  subsist  between  the  elementary  bodies.  We  have 
divided  them  into  natural  families  or  groups,  according  to  our 
idea  of  the  true  principles  which  must  govern  every  attempt 
to  create  a  natural  classification  in  any  branch  of  science  what- 
ever. In  a  word,  we  have  endeavoured  to  rely  upon  general 
and  not  upon  particular,  analogies,  and  our  classification  con- 
sequently differs  for  better  or  for  worse  from  every  one  which 
has  yet  been  proposed.  The  merit  of  having  first  suggested 
such  a  mode  of  classification  belongs  to  the  English  chemist, 
Graham,  who,  in  his  recent  treatise  upon  Chemistry,  has  divi- 
ded the  elements  into  eleven  classes,  depending  chiefly  upon 
their  isomorphous  relations.  We  will  here  quote  the  classes 
of  Graham  in  a  column  over  our  own. 


GROtrp  xiv.  4  7 

Graham. 
1st  Class.  Oxygen,  Sulphur,  Selenium,  Tellurium 
2d  Class.  Mg— Ca— Mn— Fe— Co— Ni— Zn— Cd— Cu— H— - 

Bi— Cr— Al— Gl— V— -Zn— Y— Th. 
3d  Class.  Barium,  Strontium,  Lead. 
4th  Class.  Potassium,  Sodium,  Ammonium,  Silver. 
5th  Class.  Chlorine,  Iodine,  Bromine,  Fluorine. 
6th  Class.  Nitrogen,  Phosphorus,  Arsenic,  Antimony. 
7th  Class.  Tin,  Titanium. 
8th  Class.  Gold,  Silver. 

9th  Class.  Platinum,  Palladium,  Iridium,  Osmium. 
10th  Class,  Tungsten,  Molybdenum. 
11th  Class.  Carbon,  Boron,  Silicon. 
Unclassified.  Mercury,  Cerium,  Columbium,  Rhodium,  Uran- 

ium,  Lanthanum,  (Erbium  and  Terbium.) 

1st  Class.  Oxygen,   Sulphur,  Selenium,  Tellurium,  Chlorine. 
Iodine,  Bromine,  Fluorine. 

2d  Class.  Phosphorus,  Nitrogen,  Arsenic,  Antimony. 

3d  Class.  Hydrogen,  Zinc,  Cadmium,  Magnesium. 

4th  Class.  Iron,  Manganese,  Cobalt,  Nickel,  Chromium. 

5th  Class.  Aluminum,  Glucinum,  Zirconium. 

6th  Class.  Molybdenum,  Tungsten,  Vanadium,  Columbium, 

7th  Class.  Copper,  Mercury,  Bismuth,  Palladium. 

8th  Class.  Barium,  Strontium,  Calcium,  Lead,  Silver. 

9th  Class.  Platinum,  Titanium,  Iridium,  Osmium. 

10th  Class.  Gold,  Uranium,  Rhodium,  Tin. 

11th  Class.  Potassium,  Sodium,  Lithium. 

12th  Class.  Yttrium,  Thorium. 

13th  Class.  Cerium,  Lanthanum,  Didymium,  Erbium,  Ter- 
bium. 

14th  Class.  Carbon,  Boron,  Silicon. 
We  are  likewise  indebted  to  the  suggestions  of  Dr.  Kane, 

for  several  important  changes  in  the  original  classification  of 

Graham :  thus  lead  and  silver  Were  first  associated  together 

by  the  Irish  chemist,  as  were   also  palladium  and  copper. 


4S  CHEMICAL    CLASSIFICATION. 

With  certain  other  changes  proposed  by  Kane  we  do  not  co- 
incide, as  they  are  entirely  opposed  to  our  convictions  of 
truth. 

The  tendency  of  discovery,  in  our  time,  is  to  connect  the 
different  groups  arflfthe  individual  members  of  which  they 
are  composed  more  and  more  closely  together.  Every  year 
fills  up  some  separating  chasm,  brings  to  light  new  analogies, 
and  impresses  us  yet  more  strongly  with  the  belief  that  nature 
in  truth,  is  one  in  essence,  though  many  in  form.  Perhaps  it 
will  hereafter  be  found  that  those  bodies  which  we  term  ele- 
ments are  in  reality  compound ;  that  they  are  the  resultants  of 
a  few  elementary  forces,  themselves  perhaps  but  modifications 
of  a  single  primary  force.  The  very  idea  of  matter,  reduced 
to  its  simplest  form,  is  the  idea  of  resistance,  and  the  idea  of 
resistance,  think  of  it  as  we  may,  is  only  one  form  of  the  idea 
of  force.  To  us  and  to  our  nature,  an  atom  is  a  sphere  of  force 
to  whose  centre  we  cannot  get.  This  view  of  the  constitu- 
tion of  matter,  will  at  least  afford  us  some  explanation  of  those 
analogies  which  now  seem  so  difficult  to  comprehend  ;  for  the 
resultants  of  the  same  forces  must  of  necessity  bear  some  re- 
lation and  proportion  to  one  another  ;  and  it  seems  to  us  at 
least,  that  the  assumption  of  a  few  primary  forces,  whose  in- 
numerable modifications  and  modes  of  action,  produce  all  the 
phenomena  of  material  bodies  with  which  we  are  acquainted, 
enables  us  to  form  a  simpler  and  a  clearer  idea  of  the  unity  of 
nature  than  any  hypothesis  which  has  yet  been  proposed. 

To  exemplify  at  a  glance  the  relations  of  the  several  groups 
to  each  other,  and  to  show,  at  the  same  time,  in  what  manner 
the  elements  form  a  natural  scale  of  gradation,  we  propose  to 
make  use  of  an  artifice  often  adopted  by  naturalists,  and  for 
the  suggestion  of  which  the  writer  is  indebted  to  Dr.  Torrey. 

Assuming  a  single  element,  oxygen  for  example,  as  a  cen- 
tre, we  may  draw  around  it  a  circle  of  any  convenient  radius, 
and  we  may  divide  this  circle  into  segments,  each  segment 
corresponding  to  some  particular  point  of  analogy. 

Concentric  with  this  primary  circle,  and  separated  from  it  by 


SCHEME  OF  AXilOfjlES. 


ITH.  OF    S*   W.  END1COTT. 


COMPOUNDS.  49 

a  short  interval  of  radius,  we  may  draw  another  which  shall 
serve  to  include  those  substances  which  are  connected  with 
oxygen  and  with  each  other  by  the  first  degree  of  affinity, 
and  we  may  place  each  substance  opposite  the  segment  of  the 
primary  circle  which  indicates  the  point  of  analogy  by  which 
it  is  most  closely  connected  with  oxygen.  A  third  circle,  ex- 
ternal to,  and  concentric  with  the  last,  will  include  those 
bodies  which  are  connected  with  oxygen  by  the  second  de- 
gree of  analogy,  and  so  on  for  other  circles.  Blank  segments, 
or  blank  circles  will  indicate  want  of  analogy  in  particular 
points  or  in  entire  degrees.  And  thus  we  shall  obtain  a 
graphical  illustration  of  the  connection  of  the  elements  with 
each  other,  and  of  the  degree  of  analogy  between  the  several 
groups. 

OF  THE  CLASSIFICATION  OF  COMPOUNDS. 

The  classification  of  compounds,  according  to  the  natural 
system,  obviously  depends  upon  the  previous  classification  of 
the  elements,  and  follows  readily  and  easily  from  a  knowledge 
of  the  arrangement  and  relations  of  the  elementary  groups. 
Upon  this  portion  of  our  subject  we  propose  to  be  as  brief  as 
is  consistent  with  clearness.  The  principles  of  classification 
which  we  shall  adopt  are  as  follows  : 

1.  The  compounds  of  the  members  of  group  1st  with  one 
another  are  arranged  according  to  their  molecular  types. 

2.  The  compounds  of  the  members  of  any  other  group  than 
group  1st  with  the  members  of  group  1st,  are  arranged  to- 
gether in  groups  according  to  molecular  types,  principally  and 
according  to  isomorphism,  wherever  isomorphisms  subsist. 

For  example,  we  classify  together  the  Protoxides,  Proto- 
sulphides,  Proto-selenides,  Proto-tellurides,  Proto-chlorides, 
Protiodides,  Proto-bromides,  and  Proto-fluorides  of  the  mem- 
bers of  each  natural  group  of  elements.  Supposing,  for  ex- 
ample, that  a  particular  natural  group  contains  four  elements, 
we  should  have  of  course  a  group  of  proto-amphides  of  this 
elementary  group,  consisting  of  4  x  8  =  32  individuals.    These 

5 


50  CHEMICAL    CLASSIFICATION. 

again  we  subdivide  into  eight  sub-groups,  each  sub-group  con- 
sisting (in  this  particular  instance)  of  four  individuals.  The 
sub-groups  are  arranged  according  to  their  electro-negative  or 
chlorous  constituent,  so  that  we  thus  associate  together  in  the 
same  sub-group,  all  the  protoxides  of  a  particular  class  of  el- 
ements ;  in  another  sub-group  all  the  proto-sulphides  of  the 
same  class  of  elements,  and  so  on. 

The  same  principle  is  applied  to  the  classification  of  deuto- 
amphides,  sesqui-amphides,  and  so  forth. 

As  examples  of  this  method  of  arrangement,  we  will  give 
a  few  groups  and  sub-groups  of  different  molecular  types. 

THIRD  GROUP  OF  ELEMENTS. 

Zinc,  Cadmium,  Magnesium,  Hyd7,ogen. 

GROUP  OF  PROTO-AMPHLDES. 

Sub-group  1st.  Sub-group  2d.   Sub-group  3d.  Sub-group  4th. 
ZnO  ZnS  ZnSe  ZnTe 

CdO  CdS  CdSe  CdTe 

MgO  MgS  MgSe  MgTe 

HO  HS  HSe  HTe 

Sub-group  5th.  Sub-group  6th.  Sub-group  7th.  Sub-group  Sth. 
ZnCl  Znl  ZnBr  ZnF 

CdCl  Cdl  CdBr  CdF 

MgCl  Mgl  MgBr  MgF 

HC1  HI  HBr  HF 

As  the  members  of  the  3d  group  of  elements  do  not  form 
very  distinct  compounds  with  more  than  one  equivalent  of  a 
member  of  the  first  or  amphigen  group,  we  must  refer  to  some 
other  one  of  the  elementary  groups  for  further  illustrations.  It 
will  be  immediately  observed  in  the  example  which  we  have 
already  given,  that  the  Protoxides  of  group  1st  constitute  to- 
gether a  natural  family  or  sub-group,  the  protosulphides  a  sec- 
ond sub-group  and  so  on :  hence  in  a  descriptive  work,  the 
sub-groups  should  be  treated  of  in  succession,  first  by  a  gen- 
eral account  of  their  properties  and  relations,  and  secondly  by 


COMPOUNDS.  51 

the  special  description  of  the  individuals  of  which  each  sub- 
group is  composed. 

Another  example  of  a  natural  sub-group  is  furnished  by  the 
sesquioxides  of  the  fourth  group  of  elements,  viz : 
Fe203,Mn203,Cr203,  Co203,  Ni203. 

Again  we  have  as  a  sub-group  of  another  type, 
N05,    P05,    As05,  Sb06. 

Again,  PbCl2,  IrCl2,  0sCl2,  TiCl2. 

From  this  principle  of  classification  it  follows  that  we  shall 
have  for  each  group  of  elements,  several  groups  of  com- 
pounds, with  the  members  of  group  1st,  the  number  depend- 
ing on  the  number  of  the  different  types  of  the  compounds 
formed  by  the  two  groups  with  each  other. 

Thus,  if  a  particular  group  of  elements  form  with  the  1st 
or  Amphigen  group,  compounds  of  the  types,  RA,  RA2, 
R2A3,  RA3,  it  is  clear  that  we  shall  have  four  groups  of  com- 
pounds, namely : 

1.  Proto-amphides      RA 

2.  Deuto-amphides     RA2 

3.  Sesqui-amphides     R2A, 

4.  Ter-amphides         RA3 

Each  of  these  groups  will  then  be  subdivided  into  eight 
sub-groups,  as  follows : 

Group  1st,  Proto-amphides.  Group  2d,  Deuto-amphides. 

Sub-group  1st,  Protoxides            RO  1st,  Deuotoxides         R02 

Sub-group  2d,  Proto-sulphides    RS  2d,  Deuto-sulphides   RS2 

Sub-group  3d,   Proto-selenides    B,Se  3d,   Deuto-selenides    RSe2 

Sub-group  4th,  Proto-tellurides  RTe  4th,  Deuto-tellurides  RTe2 

Sub-group  5th,  Proto-chlorides  RC1  5th,  Deuto-chlorides   RC12 

Sub-group  6th,  Prot-iodides         RI  6th,  Deut-iodides        RI2 

Sub-group  7th,  Proto-bromides  RBr  7th,  Deuto-bromides  RBr2 

Sub-group  8th,  Proto-fluorides    RF  8th,  Deuto-fluorides    RF2 

Group  3d,  Sesqui-amphides.  Group  4th,  Teramphides. 

Sub-group  1st,  Sesqui-oxides        Ro03  1st,  Teroxides  R03 

Sub-group  2d,  Sesqui-sulphides  R2S3  2d,  Tersulphides      RS3 

Sub-group  3d,  Sesqui-selenides  R2Se3  3d,  Terselenides       RSe3 

Sub-group  4th,  Sesqui-tellurides  R2Te3  4th,  Tertellurides     RTe3 


52  CHEMICAL    CLASSIFICATION. 

Sub-group  5th,  Sesqui-chlorides  R 2  CI  3      5th,  Terchlorides      RCI  - 
Sub-group  6th,  Sesqui-iodides      RoI3        6th,  Teriodides         Rig 
Sub-group  7th,  Sesqui-bromides  R2Br3      7th,  Terbromides      RBrg 
Sub-group  8th,  Sesqui-fluorides  R2F  3       8th,  Terfluorides      RF3 

3.  Compounds  which  do  not  contain  an  element  of  the  am- 
phigen  group  are  classified  together,  according  to  their  consti- 
tution and  general  relations,  into  groups.     Examples, 

NH3—  PH3—  AsH3— SbHs 
P2Cu3—  Po°Co3—  P2Ni3—  P2Mn3. 
With  the  exception  of  ammonia,  the  carburets  of  hydro- 
gen, and  one  or  two  other  substances  which  we  shall  here- 
after notice,  our  knowledge  of  the  compounds  of  the  non- 
amphigen  groups  is  as  yet  too  imperfect  to  admit  of  our  en- 
tering upon  any  generalizations  concerning  them. 

4.  Before  entering  upon  the  subject  of  the  classification  of 
double  compounds,  it  is  necessary  to  make  a  few  remarks, 
concerning  the  substitutions  of  the  elements  generally,  and 
more  particularly  concerning  the  substitutions  of  the  members 
of  the  amphigen  group  for  one  another. 

We  admit  then  generally  that  the  members  of  any  group 
are  capable  of  replacing  one  another  in  equivalent  propor- 
tions, without  destroying  the  type  of  the  particular  compound 
in  which  the  replacement  occurs,  though  the  chemical  relations 
of  the  new  compound  may  or  may  not  be  the  same  with  those 
of  the  original  from  which  it  is  derived.  We  therefore  clas- 
sify compounds  thus  derived  by  substitution  with  those  from 
which  they  are  derived,  provided  that  the  chemical  relations 
of  the  primitive  and  its  derivatives  are  not  absolutely  incom- 
patible.    Examples. 

S03—  S02S— S02C1— S02I— 

C02— CO.C1— C6.A&. 

s265-s2o3.ci2 

N05—  N08.C12 

Cr02.Cl— Mo02/CL  W03.C1. 

Under  certain  circumstances,  bodies  belonging  to  different 
groups  are  capable  of  replacing  one  another  in  combination 


COMPOUNDS. 


53 


without  altering  either  the  molecular  type  or  the  general  rela- 
tions of  the  primitive.  Such  derivatives  are  of  course  to  be 
classified  with  their  primitives.     Example. 

Acetic  acid,  C4H303  +HO. 

Chloracetic  acid,  C4Cl303  +  HO. 

5.  Finally,  the  similar  amphides  of  different  groups  may 
be  so  nearly  related  in  chemical  properties,  as  to  be  placed 
under  the  same  natural  group  or  sub-group  of  compounds. 
Examples. 

The  protoxides  of  groups  3d  and  4th,  viz  : 

ZnO,  MgO,  HO.  CdO,  FeO,  MnO,  CoO,  NiO,  CrO. 
The  sesquioxides  of  groups  4th  and  5th,  viz  : 
Fe3Oa,Mna03,Co303,Ni303,Cr30„AlaO„Cl203,ZraOs. 
The  bichlorides  of  groups  7th,  9th  and  10th,  viz  : 
PdCl3,  PtCl3,  IrCl3,  0sCl3,  TiCl3,  SnCl3. 
The  teroxides  of  groups  1st,  4th  and  6th,  viz  : 

S03,  Se03,  Te03,  Cr03,  Mn03,  V03,  W03,  Mo03. 
Certain  oxides  of  groups  1st  and  4th,  viz  : 

S„0-,  CIO.,  Mno0,—C107,  Mno07. 

6.  Double  compounds,  that  is  to  say,  bodies  composed  of 
two  others,  each  of  which  is  itself  a  compound,  are  classified 
in  a  manner  analogous  to  that  just  described  for  single  com- 
pounds, the  classification  depending  mainly  upon  the  electro- 
negative or  chlorous  compound  constituent. 

Those  double  compounds  whose  constituents  are  members 
of  the  same  natural  groups  of  single  compounds  are  classified 
together  as  a  natural  group  of  salts,  and  this  group  of  salts  is 
again  subdivided  into  eight  sub-groups,  comprising 

1.  Oxy-salts,  5.  Chloro-salts, 

2.  Sulphur-salts,  6.  Iodo-salts, 

3.  Selenio-salts,  7.  Bromo-salts, 

4.  Telluri-salts,  8.  Fluo-salts, 

wherein  the  term  salt  is  applied  exclusively  to  the  compounds 
of  bodies  relatively  acid  with  bodies  relatively  basic.  For 
example, 

5* 


54  CHEMICAL  CLASSIFICATION. 

S03,  SeO„  Te03,  Cr03,  Mn03,  Mo03,  W03, 

beftmging  to  the  same  sub-group  of  acids,  and 

ZnO,  MgO,  CdO,  HO,  FeO,  MnO,  CoO,  NaO,  CrO, 

belong  to  the  same  sub-group  of  bases,  consequently  the  sim- 
ilarly constituted  compounds  of  these  acids  and  bases  form  to- 
gether a  natural  sub-group  of  salts,  according  to  the  princi- 
ples which  we  have  adopted.  The  63  salts  which  would  thus 
be  formed,  are  subdivided  into  7  genera,  viz  :  sulphates,  sele- 
niates,  telluriates,  chromates,  manganates,  molybdates,  and 
tungstates. 

As  the  sulphates  alone  have  been  carefully  studied,  we  will 
cite  from  them  a  few  examples  of  saline  genera. 
S03+ZnO  +  7HO     $03+CoO  +  7HO      S03+MnO  +  6HO 
S03°  +  MgO+7HO    S03+NaO  +  7HO     S03  +  MnO+4HO 
S03  +  FeO  +  7HO     S03  +  CoO  +  6HO      S03+FeO-f4HO 
S03+MnO  +  7HO    S03+NaO  +  6HO      S03  +  CdO+4HO 
In  these  instances  the  sulphates  are  all  hydrated,  and  ought 
therefore  to  be  regarded  as  triple  compounds.     Their  formulae 
however  suffice  to  exhibit  their  analogies  and  the  propriety  of 
placing  them  in  the  same  genus.     The  peculiarity  of  their 
constitution  in  containing  an  atom  of  constitutional  water  has 
already  been  alluded  to. 

As  further  examples  of  natural  sub-groups  of  salts  we  may 

cite 

PtCl0+KCl     OsCl„+KCl     SnCl2  +  KCl 

IrCl~+KCl     PdcC+KCl    TicC+KCl 
which  series  of  salts  is  arranged  according  to  base,  in  conse- 
quence of  our  imperfect  knowledge  of  the  other  acids  belong- 
ing to  the  same  group   with  the  chloracids  in  the  formulas. 
The  individuals  of  this  genus  are  isomorphous. 

The  sulphur-salts  are  for  the  most  part  analogous  to  the 
oxy-salts  containing  the  same  radicals.  As  these  two  classes 
of  salts  have  been  more  extensively  and  carefully  studied 
than  any  others,  it  would  be  easy  to  fill  many  pages  with  the 
formulae  of  the  sub-groups  which  they  form.  We  shall  con- 
tent ourselves  for  the  present  by  citing  the  formulae  of  a  few 
sulphur-salts. 


COMPOUNDS.  55 

AsS5+NaS  .AsS5+2NaS.  r  AsS5+3NaS.  rSbS5  +  3BaS„ 
AsS5+KS     .AsS5+2KS     ^SbS5  +  3NaS.  |sbS5+3AgS 
CS2+CaS.  AsS3+RS.     AsS3+2RS.    AsS3+3RS 

CS2  +  SrS.  SbS3+RS.     SbS3+2RS.     SbS3+3RS 

CS2  +  BaS.  MoS3-fKS.— WS3  +  KS.    rKS  +  HS 

CS2  +  PbS.  MoS3  +  NaS— WS3  +  NaS  ^NaS  +  HS 

Cgs2+AgS.  MoS+LS— WSS  +  LS.       cBaS+HS 

£SrS+HS 
7.  The  classification  of  the  double  salts  will  obviously  de- 
pend upon  that  of  the  salts  of  which  they  are  composed,  so 
that  we  arrange  in  the  same  group,  all  double  salts  whose 
proximate  constituents  belong  to  the  same  saline  genera.  As 
examples  of  this  mode  we  may  cite  the  group  of  salts  known 
as  the  alums,  whose  formulas  are 

KO.SO3-fAUO3.3SO3  +  24aq 
KO.SOa  +  Mn203.3S03+24aq 
KO.SO  3  +  Fe263.3S03  +  24aq 
KO.SO  3  +  Cr~  0  3 .3S0  3  +  24aq 
Again,  we  have  an  exceedingly  well  defined  group  of  double 
salts  in  certain  oxalates,  represented  by 

3(K0.C203)  +  Cr2O3.3C203+6aq 
3(K0.G203)+Fe203.3C203  +  6aq 
3(KO.C203)  +  Al205.3C203  +  6aq 
and  in  the  well  known  double  sulphates, 

ZnO.S03  +KO.SO3  +6aq        MnO.S03  +KO.S03  +6aq 
MgO.S03  +  KO.SO3  +  6aq       CoO.S03  +  KO.S03  +  6aq 
CdO.S03+KO.S03+6aq        NiO.S03+KO.SOs+6aq 
FeO.S03  +KOS03  +6aq         CrO.S03  +  KO.SO  3  +6aq 

GnO.S03  +  KO.SO  3+6aq. 
No  double  compounds  of  the  other  saline  sub-groups  are 
known  to  exist,  though  there  is  every  probability  that  double 
sulphur-salts,  chloro-salts  and  so  on,  will  hereafter  be  described. 
We  are  acquainted  with  two  very  remarkable  double  salts,  one 
oL  whose  constituents  is  an  oxy-salt  and  the  other  a  sulphur- 
salt,  they  are  represented  by 


56  CHEMICAL    CLASSIFICATION. 

(WS3+KS)4-(N05+KO) 

^  (MoS5+KS)-f(N05  +  KO) 

8.  The  principles  which  we  have  laid  down  for  the  classifi- 
€ation  of  single  and  double  salts,  apply  also  to  all  compounds 
consisting  of  three  or  more  oxides,  sulphides,  chlorides,  &c.  as 
well  to  those  which  consist  of  oxides  united  to  chlorides, 
iodides  or  other  amphides.  Under  this  last  head  all  hydrated 
salts  ought  in  strictness  to  be  included,  together  with  hydrated 
amphides,  in  which  the  water  appears  to  play  a  different  part 
from  that  either  of  an  acid  or  a  base.  The  same  remark  ap- 
plies to  those  compounds  which  contain  excess  of  oxide,  chlo- 
ride or  amphide  in  general,  beyond  and  above  what  is  neces- 
sary to  constitute  a  neutral  salt  with  the  particular  acid  or  base 
in  the  compounds.  The  oxides  of  zinc,  copper  and  lead,  and 
the  proto-chloride  of  mercury  are  peculiarly  apt  to  form  com- 
pounds of  this  character,  and  the  compounds  thus  formed  we 
regard  as  precisely  analogous  to  ordinary  hydrates. 

To  finish  the  task  which  we  imposed  upon  ourselves  in  the 
commencement  of  our  essay,  it  remains  for  us  to  consider 
briefly  the  analogies  which  subsist  between  simple  and  com- 
pound bodies. 

The  discovery  of  Cyanogen,  by  Gay-Lussac,  furnished  the 
first  instance  of  a  compound  body  which  in  all  its  chemical 
relations  bore  the  most  exact  analogy  to  an  elementary  sub- 
stance. And  since  the  period  of  its  discovery  the  researches 
of  chemists  have  brought  to  light  many  other  substances  of 
greater  or  less  simplicity  of  constitution,  which  in  the  same 
manner  present  all  the  chemical  properties  and  relations  of 
true  elements.  It  becomes  then  to  us  a  matter  of  some  im- 
portance to  determine  the  principles  upon  which  these  bodies 
are  to  be  classified  and  arranged  according  to  the  principles  of 
a  natural  system,  since  it  is  clear  that  they  must  occupy,  in 
any  classification,  a  position  essentially  different  from  that  of 
an  ordinary  compound  of  two  or  more  elements.  If  we  con- 
sider for  a  moment  the  properties  of  these  compound  elements, 
if,  without  an  Hibernicism,  we  may  use  such  an  expression, 


COMPOUNDS. 


57 


we  shall  find  that,  for  the  purposes  of  classification,  they  may 
be  divided  into  two  classes,  depending  upon  their  analogies 
with  the  amphigen  group  of  our  division,  or  with  the  non- 
amphigen  groups.     Every  compound  radical  is  either  electro- 
negative or  electro-positive,  chlorous  or  zincous,  an  analogue 
of  zinc,  or  a  former  of  acids  and  bases  like  oxygen  and  chlo- 
rine.    As  a  chlorous  radical  we  may  cite  cyanogen  ;  as  a  zin- 
cous radical,  ammonium,  and  as  a  binary  compound  of  a  chlo- 
rous with  a  zincous  compound  radical  exactly  analogous  to 
chloride  of  potassium  we  may  cite  cyanide  of  ammonium. 
Show  us  a  metallic  chloride  of  a  given  molecular  type  and 
we  will  produce  a  corresponding  cyanide.     Show  us  a  salt  of 
potassium  and  we  will  place  by  its  side  a  similar  and  even  an 
isomorphous  salt  of  ammonium.     It  is  upon  these  analogies 
then  that  we  base  our  classification  of  compound  radicals. 
Those  which  like  oxygen  or  chlorine  are  capable  of  forming 
acid  or  basic  compounds  with  other  radicals,  we  associate  in 
the  same  class  with  oxygen  and  chlorine,  while  those  on  the 
contrary,  which  are  most  distinctly  acidifiable  or  basifiable 
like  metals,  we  associate  either  in  groups  by  themselves,  ac- 
cording to  their  analogies  with  each  other,  or  in  the  same 
groups  with  the  simple  substances  which  they  may  most 
strongly  resemble.     It  is  of  course  to  be  constantly  borne  in 
mind  that  compounds  like  simple  radicals  are  always  rela- 
tively chlorous  and  zincous,  and  that  the  same  substance  may 
at  one  time  act  the  part  of  an  electro-negative  or  chlorous  rad- 
ical, like  chlorine  in  a  metallic  chloride,  and  at  another  time 
that  of  an  electro-positive  or  zincous  radical,  like  chlorine  in 
chloric  acid.    Furthermore,  we  may  remark  in  this  connexion, 
that  the  position  of  an  element  when  acting  electro-negatively 
may  be  very  different  from  the  position  which  the  same  ele- 
ment occupies  when  acting  electro-positively  or   zincously. 
For  example,  electro-negative  chlorine  is  associated  by  the 
strongest  analogies  with  oxygen,  sulphur,  &c.  while  electro- 
positive or  zincous  chlorine  is  isomorphous  in  combination 


58  CHEMICAL    CLASSIFICATION. 

with  two  equivalents  of  manganese  (or  sulphur,  though  this 
last  is  rather  inferred  than  demonstrated.) 

wigain,  chlorous  sulphur  is  analogous  to  oxygen  and  the 
other  bodies  of  the  amphigen  group,  whereas  zincous  sulphur, 
as  in  sulphuric  acid,  is  isomorphous  with  the  elements  belong- 
ing to  the  fourth  or  manganese  group,  one  equivalent  repla- 
cing one  equivalent  of  metal.     Thus  the  chlorates  and  hyper- 
chlorates  are  isomorphous  with  the  corresponding  hypo-man- 
ganates  and  hyper-manganates  C105+RO  with  Mn205  +  R0 
ClO^  +  RO  with  Mn207+R0,  while  the  sulphates  andseleni- 
ates  are  isomorphous  with  the  manganates  and  chromates,  SO  3 
+  RO  and  SeO  3  +  RO  with  MnO  3  +  RO  and  CrO  3  +  RO.     The 
relative  states  in  which  bodies  exist  in  combination  have  not  suf- 
ficiently attracted  the  attention  of  chemists,  and  it  is  possible  that 
it  is  in  these  conditions  that  we  are  to  look  for  the  explanation 
of  many  phenomena  which  are  at  present  involved  in  obscurity. 
Thus  then,  briefly  and  imperfectly,  we  have  traced  through 
the  different  elementary  bodies  the  prevalence  of  the  law  of 
grades.     We  have  endeavoured  to  show  that  the  chemical 
properties  and  relations  of  all  substances  differ  only  in  degree, 
and  that  they  are  therefore  associated  together  in  natural  fam- 
ilies or  groups  according  to  the  different  degrees  of  analogies 
which  subsist  between  them.     We  have  already  stated  that  it 
is  to   Graham    we  owe  the   first  suggestion  of  a  natural 
system  of  classification.     We  regard  that  idea  as  one  of  the 
most  important  in  the  whole  history  of  chemical  science,  and 
as  likely  to  lead  us  to  deeper  and  clearer  views  upon  almost 
every  point  in  theoretic  chemistry,  than  we  have  yet  been  able 
to  attain.     A  just  and  comprehensive  system  of  classification 
has  ever  been  a  most  powerful  instrument  in  the  advancement 
of  a  science.     As  our  knowledge  advances,  many  changes  will 
be  made  in  the  groups  of  elements  at  present  adopted  as  pri- 
mary, many  chasms  will  be  filled  up,  many  new  points  of 
analogy  discovered,  many  superficial  resemblances  detected 
and  exposed,  but  the  principles  and  the  main  features  of  the 
natural  system  of  arrangement  will,  we  most  firmly  believe, 


COMPOUNDS.  59 

remain  unchanged.  And  as  with  every  new  discovery,  we 
obtain  a  farther  and  clearer  insight  into  the  mysteries  of  na- 
ture, we  believe  that  the  law  of  grades  will  become  more  and 
more  apparent,  till  at  last  it  shall  be  acknowledged  that  in  the 
Inorganic  as  well  as  in  the  Organic  kingdoms,  Natura  non 
facit  saitum. 


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